how does curley use/manipulate lennie?

Curley has a major case of "small guy complex". He sees that Lennie has mental shortcomings and delights in intimidating him. Curley also thinks that Lennie, a big man, won't defend himself. He goes after Lennie because Lennie smiles while at a joke made at Curley's expense. Lennie doesn't defend himself until George tells him to. Lennie then crushes Curley's hand.