Upon stating that something is (adjective) and having another person turn this back on you by stating that YOU are (adjective), you will respond that their face is (adjective). They will try to counter that your mother is (adjective), but upon stating that their mother is a whore, you will win, because nothing beats that.
Your opponent might predict where this is going early on and try to break order, but this just shows them to be a fucking douche.
Originates from a strip in the Gigaville webcomic.
B: You're stupid.
A: Your face is stupid.
B: Your mom's stupid.
A: Your mom's a whore.
B: Oh yeah, well... shit.