I know I am but what are you?
The opposite of the widely known, stupid comeback, This will usaully get your offendor to say something stupid about themselves.
Person 1: You suck eggs!
Person 2: I know I am but what are you?
Person 1: A dipwad.
Person 2: Exactly
Person 2: I know I am but what are you?
Person 1: A dipwad.
Person 2: Exactly