Why does Crooks attempt to bait and frighten Lennie?

In chapter 4, Lennie walks into Crooks's room uninvited, which initially upsets Crooks, who is the only black man on the ranch and is not used to having visitors. As the only black man on the ranch, Crooks suffers from racial discrimination and occupies the lowest social position on the farm. He is forced to live segregated from the other workers and resents the fact that he is the most oppressed man on the ranch. When Lennie enters his room, Crooks realizes that he is in a uniquely powerful position and feels superior to Lennie, who is mentally handicapped. Crooks begins to upset and worry Lennie by hypothetically asking him questions about what would happen if George abandoned him. Crooks's callous actions reflect his own treatment on the ranch and reveal his resentment towards white, privileged individuals like Lennie. Since Lennie has a close friend in George, Crooks's awful treatment may also reflect his jealousy and bitterness. Crooks desperately wishes to have a companion and friend like George and suffers from extreme loneliness. Crooks's actions may also reflect how he has been taught by others to wield power. Individuals like Curley use their power to oppress and intimidate others, which is exactly what Crooks does when he is given the opportunity.

Crooks occupies the very lowest position on the ranch. As a disabled black man he's completely isolated from everyone else. Yet in the figure of Lennie, Crooks sees the one person on the ranch to whom he can feel in some way superior. Lennie may be a white man, but with the mental age of a child he's at a distinct disadvantage to Crooks. Crooks takes this rare opportunity to assert control over another human being. He acts cruelly towards Lennie, making him think that George will one day leave the ranch without him. Crooks feels deeply resentful towards Lennie for having such a close relationship with George; he himself doesn't have a friend in the world. So he takes out all his bitterness, anger, and frustration on Lennie, who because of his learning disabilities is an easy target.