Not exactly a "ptui" situation, but: my college roommate had been trying an experimental treatment for hemerhoids...chapstick. (Don't blame me; it wasn't my idea, and I didn't even know until later.) The kid from across the hall was bumming around in our room, picked up the chapstick,(as if that wasn't a little crass anyhow)and used it on his lips. I had no idea why my roommate was laughing so hard until he explained later.