This is something that I play a lot with my friends back home. It's pretty simple and usually entertaining.... but that could be for a couple of reasons.
All you do is propose a "what if" question and everyone says what they would do. It can be something simple, ridiculous, creepy, anything. I'll go first.
What if you woke up one morning and gravity was reversed.... your bed, dresser, you, everything was on the ceiling.