Dirty Sanchez (etymological)
A Dirty Sanchez occurs when the passive partner (male or female) is sodomized and a coating of mucus/feces/lube remains on the shaft of the active partner's penis. He pulls out and the passive partner fellates him, drawing the member into his/her mouth through tightly pursed lips. This acts to squeegee the matter from the penis into a thin line or bead
encircling the mouth. It forms a
John Waters's moustache-like deposit on the recipient's upper lip like the moustache on a Mexican guy (e.g., from a 1930s movie; hence "Sanchez"), or
John Waters. (A "Filthy Waters" is equally descriptive, but that term hasn't caught on perhaps due to its being a bit esoteric.)