Our lovely Nell gave me a ton to choose from, so let's start with a classic: truth or dare.
Reply with your character saying either "Truth" or "Dare." Other characters will reply to you with a truth or dare, which your character will then have to reply to. If you do give a character a truth or dare, you have to post as well and offer your character up to truths and dares!
Since this is just a game, all information in this thread is OOC and for the lulz. Your character cannot know these things unless the other player gives you permission – it could give you some plot ideas!