In our matroom, there are a few dirty tricks that go on when someone isn't ready for it. For example:

MEEPS: This is when you sneak up on someone from behind and poke them in the eyeball while saying "meep!"

BIPS: Simply put, this is when you hit someone in the junk. Style points are awarded for a clever set-up.

Anyone have any other dirty tricks I can use on my unsuspecting friends?