In Chapter Two of Of Mice and Men, George becomes angry with his disillusionment about his and Lennie's new jobs: "Looks like we was gonna have fun." Already alienated by the antagonism of Curley, George realizes from what Candy has told him that Lennie will have trouble with Curley, who views him as an adversary. So, he warns Lennie to avoid Curley by not speaking to him and by moving away from him if necessary, telling Lennie, "Don't let him pull you in."
Then, after Curley's wife appears in the doorway, looking like the "tart" that Candy has described her as, George becomes even more irritated and frustrated with his and Lennie's situations. He warns Lennie about not looking at her or having anything to do with her:
"Don't you even take a look at that b---. I don't care what she says and what she does. I seen 'em poison before, but I never seen no piece of jail bait worse than her. You leave her be."
Lennie protests that he has done nothing, but George scolds him for looking at her legs. When Lennie says that he meant no harm, George again cautions him, telling Lennie she is
"a rat-trap if I ever seen one. You let Curley take the rap. He let himself in for it...."
Curley's wife is like a rat-trap as she is one who will snare a man and he will not escape without serious injury or death. There is no good that can come from being around Curley's wife, so George tells Lennie to just let her bring about her own trouble with her husband: "let Curley take the rap."
This naturalistic portrayal of the characters depicts Lennie and George immediately being alienated, and it is this alienation that angers George. The symbolism of the sunshine being cut off when Curley's wife appears in the doorway, also, cannot be missed. The forces of evil--Curley as a pugnacious man and his wife as an Eve, a temptress--conflicts with the forces of good.
The work to which George refers for Curley is taming his wife. George has now had the opportunity to see her and he can tell, she is no settled wife. George makes a genuine observation that this woman might still be on the hunt for her man in this world even though she is married to Curley already.
I think his anger comes from the idea that if Lennie gets in trouble with this gal, it's trouble for the both of them. If they both get in trouble, the chance to save some money and buy a place together is a lot less likely than it was even before they arrived.