I love everything said in "My Man Godfrey".
Ooh, and The Philadelphia Story:
Liz: They have a cousin who is definitly crazy.
Mike: How do you know?
Liz: Dinah told me.
Mike: Dinah would know!
Mike: Doggonit C.K. Dexter Haven, either I'm gunna sock you or you're gunna sock me!
Dexter: Shall we toss a coin?
Bringing Up Baby:
Aunt Elizabeth: You look perfectly ridiculous in those clothes.
David: These aren't my clothes. I've lost my clothes.
Aunt Elizabeth: Well, why are you wearing these clothes.
David: Because I just went GAY all of a sudden!
David: I'm a nut from Brazil!
and North by Northwest:
Roger: Not that I mind a slight case of abduction now and then, but I have tickets to the theater this evening, to a show I was looking forward to, and I get well, kind of unreasonable about things like that.
Van Dam: With such expert play acting you make this very room a theater.