Tommy thumps his hand on the door, grinning. "Hey, no need to get down, man. It's only a knock knock joke."

He manages to hold his snickers in for a good five seconds, because the punchline doesn't work as well if you're cackling. Of course, Tommy's self-control being what it is, he falls over from trying to keep it in, and ends up crouching on the ground, laughing.

"Oh maaaaan, I wish I could see your face!"

He really is going to regret this later, isn't he?