You find a pinkish vial that looks very odd. "The Recessive Cock Potion", you read on the label. Taking it to the till, you ask the girl there, "What's this do?"
"It's a sort of extreme hormonal suppressant," she explains. "Take it and your body will form the opposite genitalia to what it touches. I think neutral sex acts like anal or oral speed up the process, apparently."
You're suddenly overtaken by curious excitement. "How much?" you ask.
"5 bucks," she replies. You hand over the money quickly, and start planning something.
"Hey, Paul?" you say down the phone.
"Yeah?"
"Do you, uh... wanna come over and have some fun? I've got something special I wanna try..."