One deck of SET® cards, and 2 or more players.
Play like regular SET®, with the following exception: Instead of calling "SET!" when you find a Set, you must be the first person to slap one hand down on each of two of the three cards, and your forehead down on the third.
We have not play-tested this game.
Well, now we have. Robert played Bonk style while the rest of us played as usual. It turned out to be a pretty good strategy -- Robert won (which he doesn't do too often). But we think the reason he won is that we were so distracted by watching him smack his forehead down on the table.