You've probably all come across this game in some form or other and the rules are very simple. Basically you write your character's reaction were they to wake up in bed next to the person above them.

Let the hilarity ensue!

Covers her eyes with her hand and searches blindly for her wand. "Somebody tell why there's a Basilisk in my bed! I want this explained! NOW!"

"Prongs! What did you drop in my pumpkin juice last night! Bastard >.>"

"This never happened. I refuse to believe it."