Do what @[Dungeoneering] said, I've tried it a lot its hella fun. Or:
Get a 50 cent coin (If Australian), IF American, get a coin.
Go to a small table, you go on one side, other mate goes on other side
Make coin spin in middle of the table, and you have to keep flicking it while its spinning
Whoever make it stop spinning, gets owned like this:
hold the coin on the table, as if you're about to move it with your palm, but like fling it
the other person has to put their fingers on the table, so the knuckles have to be faced on the table.
You fling it to their knuckles, and they'll bleed or get really hurt!