At the end of this chapter, George is worried about two people. They are Curley and Curley's wife.
He is worried about Curley because he is such a bad tempered man. And he is worried about Curley because Curley clearly dislikes Lennie. George worries that something bad will happen between the two of them.
He is worried about Curley's wife because she is always coming around and sort of making like she's coming on to the workers. It's like she's using them to make her husband mad.
As it turns out, he had good reason to be worried, because they both contribute to Lennie's death in their own ways.
George's reason for worry about these two has much to do with Lennie.
Lennie likes soft things and has struggled with women in the past. He sees something soft and wants to touch it, sometimes he touches too hard.
Curley has what I like to call 'little man syndrome', he has a chip on his shoulder and is ready to prove it to any bigger man. This bigger man could be Lennie.
George is anticipating two of Lennie's character traits being put into play by these individuals. If you ever see that happen, you could call the end of chapter 2 a little bit of foreshadowing.
In short, Curley and Curley's wife. As they are getting settled in the bunkhouse, Curley's wife stops in and asks if anyone has seen her husband, acting flirty. Lennie can't keep his eyes off of her, and this worries George - this is what got him in trouble in Weed right before they got this job.
Curley enters, looking for Slim, and almost immediately sidles up to Lennie and confronts him, mocking his mental handicap, little guy vs. big guy. George warns Lennie to stay away from both of them.