George is primarily bossy with Lennie, and, in particular, when he wants to be sure Lennie understands exactly how to behave or when Lennie needs precise instructions about what to do. For example, when they are camping by the natural pool at the Salinas River at the beginning of the story, George gives Lennie's specific orders about getting ready for bed:
Bring your bindle over here by the fire. It's gonna be nice sleepin' here. Lookin' up, and the leaves. Don't build up no more fire.
Lennie, on the whole, does not resent being bossed around by George as long as George is not trying to take an animal from him. He very much needs the kind of detailed instructions George gives him.
When they get to the ranch and meet Curley, George worries about what might happen if Curley provokes a fight with Lennie. He tells Lennie he is scared, but he also tells him to stay away from Curley. He bosses Lennie around by going over with him very carefully what he should do if he gets into trouble, repeating to him earlier orders that he hide in the brush by the pool:
Hide till I come for you. Don't let nobody see you. Hide in the brush by the river. Say that over.
Other than Lennie, George has little desire to boss anyone around. He gets along well with Slim, and he doesn't become involved over whether or not to shoot Candy's old dog. George doesn't like to be pushed around and stands up to Curley as far as he dares—as he stands up to other people. But as long as he is not stepped on, George is fine with letting things go. His bossiness is for Lennie and is necessary.