Specifically, in chapter four of Of Mice and Men, Curley's wife threatens Crook with her ability to tell white men that he, a black man, did something sexually to her.  It isn't directly stated as such, but it is definitely implied.

Crooks stands up to her and is immediately put back in his place by her.  She says:

She turned on him in scorn.  "Listen, Nigger," she said.  "You know what I can do to you if you open your trap?"

And again:

She closed on him.  "You know what I could do?"

Crooks reacts:

Crooks seemed to grow smaller, and he pressed himself against the wall.  "Yes, ma'am."

And she finishes him off:

"Well, you keep your place then, Nigger.  I could get you strung up on a tree so easy it ain't even funny."

Her use of the perjorative that ignorant whites use for blacks, and her reference to lynching, makes her meaning clear--all she has to do is say Crooks tried something sexual with her, and he would be hanged.  He is, figuratively speaking, put back into the place society keeps him in.

At the end of Chapter 4, Crooks is a totally defeated man.  He has had to give in to Curley's wife and he feels the fact that he is completely powerless.  You can see this symbolized in the fact that he starts putting liniment on his back (his disability) after she leaves.

The reason his attitude changes is that Curley's wife has reminded him that he is a nothing.  Up until that point, he had been sharing in Lennie's dream.  But when Curley's wife treated him the way she did, he was reminded that he was only a black man and that any white person could pretty much do what they want to him.

Lennie and Curley's wife both find themselves separated from the rest of the group for different reasons. With Lennie, he's just not able to socially keep up and compete with the other guys. With Curley's wife, she just doesn't have any girlfriends. Because of this separation, they both feel vunerable, lonely, and abandoned. This separation can be shown through their discussion in chapter 5:

"Why can't I talk to you? I never get to talk to nobody. I get awful lonely."

Lennie said, "Well, I ain't supposed to talk to you or nothing.

Further on, we see that they both have incredible dreams that they stake their life hope in. Curley's wife says:

Could been in the movies, an' had nice clothes - all them nice clothes they wear. An' I coulda sat in them big hotels, an' had pitcher took of me.

Lennie's dream is different, but serves the same purpose:

We gonna have a little place... We gonna have a house an' a garden and a place for alfalfa, an' that alfalfa is for the rabbits, an' T take a sack and get it all fulla alfalfa and then I take it to the rabbits.

Obviously, they both have hope, although for each the hope is truly an unrealistic one.

Hope that helps.

Steinbeck, who in his youth came into conflict with his exacting mother, often portrays women as Eve-types.  Such a woman is Curley's wife.  Craving attention, she enters the world of the men, the ranch house, first on the pretext of finding her husband.  In Chapter 5 as the men play horseshoes outside, she sneaks into the barn and catches Lennie holding his dead puppy.  In a panic, he shovels hay over the puppy to hide it. From her previous encounter with Lennie, she knows that he is dim-witted, but is also excited by his brute strength, so she reveals to him that she knows what has happened to Curley's hand.  But, Lennie, who fears her because of George's warnings, refuses to talk to her.  Curley wife then takes advantage of his silence and talks to him. Still, Lennie tries to resist her temptations to talk:

'Well, I ain't supposed to talk to you or nothing.....George's scared that I'll get in trouble.'

With this confession, the temptress moves closer to him, speaking "soothingly" about the dead puppy.  She tells him that he can talk with her since the other men are preoccupied with their games.  When Lennie persists in his resistance, she becomes angry, insisting that she is doing no harm.  She speaks of her wish to be an actress and reveals that she really does not like Curley; however, she is not worried about Curley finding out since Lennie is slow and will forget what she has said.  Having thus confided in Lennie, she moves closer. Weakening under her feminine wiles, Lennie "sighs deeply," and continues his ritualistic recitation about rabbits revealing his witless conditioning.

Learning that Lennie loves to pet soft things, she tempts him with her hair, enjoying domination of a man. But, when Lennie becomes too rough, she cries out, making Lennie angry.  He has become afraid that George will hear, so he tries to quiet her by shaking her.  Unfortunately his brute strength has broken her neck.  "Bewildered," Lennie finally concludes, "I done a bad thing,...George'll be mad."  To symbolize the evil of Curley's wife having lured Lennie into his sin, Steinbeck describes her as lying "with a half-covering of yellow hay" with reddened lips parted. [yellow as symbolic of evil.]

When Curley learns that his wife is dead, he does not even bend over her body, the source of his sin, too.  Instead, he seeks revenge upon Lennie:

'I know he done it.....I'm gonna get him.  I'm going for my shotgun....I'll shoot 'im in the guts.'  He ran furiously out of the barn.

Slim tells George that Curley is still mad about his hand and will try to kill Lennie even if they bring him in and have him locked up.  When Curley reenters the barn, George begs him to not shoot Lennie.

'Dont shoot 'im?' Curley cried. 'He got Carlson's Luger. 'Course we'll shoot 'im.'

In an effort to distract Curley from his purpose, Slim says, "'Curley--maybe you better stay her with your wife.'"  Curley reddens, knowing what the others think.  Still, he replies,

'I'm goin'....I'm gonna shoot the guts outa that big bastard myself, even if I only got one hand.  I'm gonna get 'im.

Clearly, it is evident that Curley's desire to avenge himself against Lennie who injured his hand and to satisfy his egotistical desires is dominant in his mind. Lennie, again, is the victim of his mentally disabled nature despite his conditioning by George.

In Of Mice and Men, George and Lennie have completely different reactions to Curley's wife. While George calls her a "tramp," Lennie's says, "She's purty." George immediately senses the danger Curley's wife presents and commands Lennie to stay away from her. He is vehement with this telling Lennie, "Don't you even look at that bitch ... I never seen no piece of jail bait worse than her."

Lennie, despite his instant attraction to her (George says, "[W]hen she was standin' in the doorway showin' her legs, you wasn't lookin' the other way, neither."], also recognizes the danger of the situation and begs George to leave the ranch saying, "It's mean here." 

In fact, Curley's wife leads to all of the trouble Lennie has on the ranch. It's her fault Curley enters the bunkhouse when Lennie crushes the small man's hand. And it's her who tells Lennie to feel her soft hair, which eventually leads to Lennie snapping her neck on accident.

When Lennie first sees Curley's Wife, he comments that she is pretty, or "purty." George then warns Lennie to keep away from her. She is, after all, the wife of the boss's very jealous son.

Later in the novel, Lennie is in the barn with a puppy that he has accidentally killed, and Curley's Wife walks in. Lennie tries not to be drawn into a conversation with Curley's Wife, and tells her it's because "George says you'll get us in a mess." He then, at her invitation, starts stroking her hair, commenting "that's nice," before he accidentally breaks her neck after she starts screaming when he strokes too hard.

Before he breaks her neck, he puts his hand over her mouth to muffle her screams, and says angrily to her that "You gonna get me in trouble." This is an echo of the story George earlier related to Slim about Lennie stroking a woman's red dress too hard back in Weed and the woman claiming rape.

In summary, these brief comments are the only comments Lennie makes about Curley's Wife. He tells George that she is pretty, and he tells her that he can't talk to her because she'll get him "in a mess," which he tells her again just before he breaks her neck.

If you're interested in learning more about Curley's wife, I've provided a link to a copy of a letter that Steinbeck wrote to an actress who was playing Curley's wife in a stage adaptation of the story. In the letter, Steinbeck explains the character from his perspective.

In John Steinbeck's Of Mice and Men, Curley and his wife have a dysfunctional relationship and marriage. Both Curley and his wife are insecure and discontent in their own respective ways.

Curley feels the need to assert his masculinity by bullying others and starting fights. He is insecure about his manhood, and as a result, he is very possessive of his wife. The fact that she is not given a name of her own and is referred to as "Curley's wife" emphasizes that she is his possession. He controls her and does not allow her to associate with anyone on the ranch. He is suspicious and constantly accuses the men on the ranch of flirting with his wife. He keeps one hand in a glove filled with Vaseline and says he does so to keep the hand soft for his wife. This, along with his frequent visits to the local brothel, suggests that he is impotent and unable to satisfy his wife sexually, which could certainly explain his constant rage, jealousy, and feelings of inferiority.

Curley's wife is lonely and unhappy in her marriage. She knows she is good-looking and uses her physical attractiveness to manipulate others. She dresses provocatively and flirts with the men on the ranch in hopes of making her husband jealous. She becomes frustrated when they do not respond for fear of being fired and/or beaten by Curley. She feels rejected by Curley and sexually unfulfilled, causing her to seek attention and affection from other men. She is lonely and isolated because of her husband's controlling, possessive behavior.

Both Curley and his wife share many negative traits. They are both immature, selfish, and insecure. They are both cruel to others and absorbed with themselves. They both have poor self-images: Curley feels like he is not manly enough, and his wife feels undesired by her husband. They both flaunt what they believe to be their strengths: Curley flaunts his ability to fight, and his wife flaunts her good looks.

Overall, their relationship and marriage are unhealthy and dysfunctional. Curley spends much of his time controlling and alienating his wife, and she is preoccupied with making her husband jealous and seeking to fill the emotional and physical voids left by him.

In the story, the relationship between Lennie and Curley’s wife is that she lets him stroke her hair and he kills her.  Symbolically, they hold a deeper connection as two tragically doomed characters who have impossible dreams.

Poor Lennie!  He is an innocent soul.  Curley’s wife is a bit of a flirt and desperately wants to be noticed.  Together, they are a formula for trouble!  Yet both of these characters are linked in their commonalities: both are simple, yet have big unachievable dreams.  They are also tragically linked, since Lennie kills her accidentally.

Lennie is like a child.  He does not forsee the consequences of his actions.  Curley’s wife is childlike in her own way.  She feels ignored and trapped.  She does not like life on the ranch, and she does not like the way Curley treats her.  In chapter 5, she tells Lennie about her dream as he tells her about his.

“Nother time I met a guy, an’ he was in pitchers.   … He says he was gonna put me in the movies.  Says I was a natural.”

Curley’s wife’s dream is no more achievable than Lennie’s.  She dreams of movie stardom, he dreams of rabbits.

In chapter 1, Lennie says,

"I remember about the rabbits, George."

This is an example both of Lennie’s childlike nature and his dream.  George dismisses his statement, even though it is George who wove this tale of the future for Lennie to have something to dream about.

Curley’s wife is also dreaming of a better life.  She is lonely, even though she is surrounded by the ranch hands.  She seems drawn to Lennie in a way.  She comments in chapter 5,

“You’re nuts,” she said.  “But you’re a kinda nice falla.  Jus’ like a big baby.  But a person can see kind what you mean.”

Ironically, it is this connection that dooms the two of them.  Lennie accidentally kills her stroking her hair.

Curley takes an instant dislike to Lennie, or at least sees him as a perfect victim for his pugilistic mentality. Lennie is a big man who is unaware of his strength and is childlike in his speech and mannerisms. Curley is small and mean. As Candy says-

Curley’s like a lot of little guys. He hates big guys. He’s alla time picking scraps with big guys. Kind of like he’s mad at ‘em because he ain’t a big guy. (pg 28)

George warns Lennie to stay away from Curley but it is inevitable that their paths will cross. George, Lennie and Candy have been discussing their dream of their own place when Curley bursts in looking for his wife. Lennie is smiling to himself with the prospect of tending the rabbits when Curley directs his rage to him-

No big son-of-a-bitch is gonna laugh at me. (pg 62)

 Lennie puts out his hand to defend himself from Curley’s blows. At George’s command, ‘Get him, Lennie.’ –

 ‘Curley’s fist was swinging when Lennie reached for it. The next minute Curley was flopping like a fish on a line, and his closed fist was lost in lennie’s big hand.(p63)

Curley agrees to cover up the incident as a machine accident, but his desire for revenge is enough to make him lead the posse after the death of his wife, intent to make Lennie suffer-

 I’ll shoot him in the guts. (p95)

Curley's aggressive behavior always suggests the possibility of violence no matter who he is with. When George and Lennie first meet him, Curley is aggressive and demands that Lennie should speak for himself. Curley leaves and the swamper explains why Curley might be more inclined to pick a fight with Lennie: 

Well . . . . tell you what. Curley’s like alot of little guys. He hates big guys. He’s alla time picking scraps with big guys. Kind of like he’s mad at ‘em because he ain’t a big guy. You seen little guys like that, ain’t you? Always scrappy? 

At the end of Chapter 3, Curley is frustrated because he can not keep track of his wife. He gets into an argument with Slim and Carlson about it. Lennie watches with a grin on his face. Lennie is still smiling absentmindedly because he is thinking of the rabbits. Curley thinks Lennie is mocking him. Curley starts throwing punches. Lennie is frightened but will not retaliate until George tells him to. Lennie gets the green light and catches a punch and crushes Curley's hand. This scene is the most overt display of the violence between these two characters. And it had all been instigated by Curley. Lennie, being as strong as a bull, has a great potential for violence but he never has evil intentions. Curley is quite the opposite. He has the potential for violence and his intentions are evil, or at least self-serving. He fights to assert his manhood. Lennie would have no problem with others perceiving him as a harmless, peaceful man.