face in ass
You say face in ass at the end of a joke like you're the punchline and the other person is the punch.
He made a joke about my hair, and I said face in ass like I was the king of insults.
She told a joke about my pants, and I replied with face in ass like I was a comedy legend.
He made fun of my breakfast, and I said face in ass so hard, it scared the dog.