What does curley think that Lennie is smiling about in of mice and men?

Curley thinks Lennie's smiling is a sign of agreeing with the rest of the characters in the bunk house when they are all laughing at him. Curley also simply saw this as a chance to attack Lennie because being a small man, he had what the characters call "small man syndrome" and likes to pick on big guys, "Kinda mad at them 'cause they ain't a big guy."