Why does Lennie want to leave the farm?

When Curley first meets Lennie and George, he begins questioning the two men and George answers for Lennie, knowing that Lennie is unintelligent and might say something inaccurate or inappropriate. Curley then notices that Lennie is not answering any of his questions and becomes hostile towards the two men. George is forced to defend his friend and warns Lennie to avoid Curley at all costs after Curley leaves the bunkhouse. George also tells Lennie that Curley will cause them trouble before Candy elaborates on Curley's pugnacious personality. When Curley's wife enters the bunkhouse looking for her husband, Lennie admires her and smiles in her direction. After Curly's wife leaves, George refers to her as "jail bait" and warns Lennie to never speak to her. Lennie responds by saying,

"I don't like this place, George. This ain't no good place. I wanna get outa here...Le's go, George. Le's get outa here. It's mean here."

Lennie clearly feels threatened being at the ranch and fears that he will make a tragic mistake. After experiencing Curley's antagonistic nature and being told that he must avoid Curley's wife, Lennie does not feel safe being on the farm, which is why he wants to leave immediately.