When you punch the girl in the back of the head or neck while in the shower so the blood doesn't get everywhere and you fuck her in the ass and yell "Ricky Ticky Tabby"
Yo, Did you see tony give that bitch the mongoose at the party last weekend ?
The act of, while wearing boxers, pulling up your flaccid penis so that only the head is sticking out, being held against your abdomen by the waistband of your boxers.
I did The Mongoose in the locker room today before football practice. My friends all shared in horrified laughter