Un Culo Loco
The form of taking a body shot of tequila. The female participant has a line of salt poured below her butthole. A tequila shot is then poured into the anus, and a lime placed at the top between both cheeks. The other participant then licks the lime, slurps the shot out of the anus and finishes with no hands.
I went to a quinceañera and I asked if anyone wanted some Un Culo Locos. I was never invited back.