Best "Gotcha"

What's your favorite "gotcha" moment in a movie?

Maybe gotcha isn't the right word for it, but I'm primarily thinking of moments of dialogue where a character makes a point that essentially shuts down any argument from whoever their talking to.

Like one of my favorites (and the reason I thought of posting this) is in Pulp Fiction when Jules and Vincent are discussing foot massages. Jules insists there's nothing inherently sexual about them, and then Vincent, after asking Jules if he's given any foot massages before, and if he's any good at them, hits Jules (the self proclaimed "foot fucking master") with "Would you give a guy a foot massage?" to which Jules' only response is "Fuck you".