The Clown switcheroo is when one person blindfolds their sexual partner and begins to have anal sex with them. Eventually, the one who isn't being penetrated will say they have to go to the bathroom.
He will leave the room, and his friend in a clown suit will enter the room, and begin having anal sex with the blindfolded one. Eventually, the blindfolded one will look around and see a clown.
Hilarity and lawsuits ensue, results may vary.