Cincinnati Shoe Shampoo
Emptying your used condoms in somebody else's shoes. Typically done if the victim of the Cincinnati Shoe Shampoo interrupted a sexual act of the perpetrator or did something equally as offensive to the perpetrator.
Dude #1: "Your friend busted in on me and my girl doing the nasty so I gave him a Cincinnati Shoe Shampoo this morning."
Dude #2: "Gross dude, his feet probably smell like a protein shake now."
Dude #2: "Gross dude, his feet probably smell like a protein shake now."