Mao is a card game, the point of which is to figure out the rules. Players give each other penalty cards when someone breaks a rule. The winner of each hand gets to add a new rule every time. This is mostly a game about asserting your superiority over those who don't know how to play, but it's really damn fun to watch your friends go completely postal when they end up with 11 cards in their hand by the end of the game!

The only rule I can tell you is this one.

Watch for my upcoming node How to Play Mao, in which I will tell you how to play the game without telling you a single rule.