I know you are but what am I?
The best comeback to ever exist. It beats 'your mom' and makes your enemy cry.
He said I was a loser. I said, 'I know you are, but what am I?' and he died.
She said I was a dork. I said, 'I know you are, but what am I?' and she cried.
He said I was a failure. I said, 'I know you are, but what am I?' and he quit.