That he wont get to tend the rabbits.
Lennie fears that George will no longer let him tend the rabbits. This punishment is especially terrifying to Lennie because it jeopardizes his dream of living on a farm with George and tending the rabbits.
Curley thinks that Lennie was laughing at him (when he wasn't) and he has been wanting to pick a fight with Lennie because he dislikes people taller than him because he isn't very tall himself.
At first Lennie doesn't fight back, but then George says get Curley to Lennie so Lennie grabs Curley's fist and breaks his hand and doesn't let go until George starts slapping him.
Curley wanted to fight George I think, so he picked on Lennie. He hit Lennie a couple times and then Lennie stopped a punch in mid-air and squeezed Curley fist and brokenit ending his boxing career. Then Lennie Lille Curleys wife and he runs away and George kills him. :)
Lennie fears that he will not be able to tend the rabbits if he hurts Curley, as George has promised. He is also scared of getting in trouble with George and not being able to achieve his dream of owning a farm with rabbits.
George thinks he will probably be tangling with Curley because Curley is aggressive and constantly looking for a fight, especially with bigger guys like Lennie. George knows that Lennie's strength may provoke Curley, leading to a confrontation.
George tells Lennie to fight back and defend himself if Curley hits him. George wants Lennie to stand up for himself and not allow others to take advantage of him.
One warning that George give Lennie is to stay away from Curley because he fears that if Curley tries to fight with Lennie, Lennie will hurt Curley, and they will lose their jobs. He also says to stay away from Curley's wife.
George advises Lennie to steer clear of Curley because he is a bully with a quick temper. He warns Lennie to avoid confrontation with Curley to prevent trouble.
George and Lennie clash with Curley, the boss's son on the ranch where they work. Curley is aggressive and confrontational, leading to tension and conflict between them throughout the story.
Well at first he tells him to stay away from him, but when he starts to get punched by him he says to fight him.Two things that George tells Lennie to do with regards to Curley are to "keep his distance" and "stick up for himself".
Curley attacks Lennie out of rage and insecurity. He is a small man who feels threatened by Lennie's size and strength, and he targets Lennie in order to assert his dominance over him and prove his own toughness to the other ranch workers. Curley's aggressive behavior reflects his own feelings of inadequacy and a desire to prove himself.