Hot Potato is a pretty straightforward mini-game: someone gets the potato, which explodes after a set amount of time. To pass it to other players, just smack them! The potato passes instantly, and it becomes very important to avoid the new potato-holder...they could just pass it back before the spud explodes! It's an oddly intense mini-game, and a great way to kill some time with friends.
Interested in trying it out? Hit up the Hot Potato thread! It is 1.8-compatible, and ready to play. Enjoy!