Famous Western movie
line , spoken by Gary Cooper
in The Virginian
. It's used to respond to an insupportable insult
. It very succinctly sums up the sentiment:
"You must be joking or a simpleton to say something like that to me, knowing perfectly well that it gives me grounds to blow your head off. So I'm hip to the fact that it was all a big joke, but you should be more careful and smile when you make a big joke, or someone less serene and centered than myself will soon kill you, you son of a bitch."
(Sort of the flipside of "God love them"