Race for Pink Slips

When you and your girlfriend challenge another couple to "Race for Pink Slips" - It is like a foursome, but instead you all have sex in one room, only with your partner: First guy to finish, wins, and he gets to take the other guys girlfriend as a reward.

Similar to racing for pinks in relation to cars

The ultimate bet in terms of personal confidence in an illegal Street race or the like. Two racers put their cars on the line by offering their registration slips as winnings. The winner of the resulting race wins the opponents car for good. This is exhibited in some of the Fast and Furious movies.