Punchlining
The act of saying something absurd when someone enters a room so as to make them think that you're discussing something very bizarre.
Example:
When Pat came into the room, Joe engaged in punchlining him when he said out of nowhere "and that's the last time I ever set a penguin on fire in my bathroom!".
When Pat came into the room, Joe engaged in punchlining him when he said out of nowhere "and that's the last time I ever set a penguin on fire in my bathroom!".