The looks of both the thug and Superman's faces when the former tries to shoot him.
Luthor: Kitty, what did my father always used to say?
Kitty: "You're losing your hair"?
Kitty: "Get out"?
When Lane is unknowingly snooping around Lex's yacht, and he just walks in in a bathrobe brushing his teeth. So unusual to see the criminal mastermind caught off guard like that. Even he can't believe who he's seeing, as he says "Lois Lane?" in disbelief, toothbrush still in mouth.