The act of urinating while engaged in anal intercourse aka peeing in the butt.
The Sloppy Thomma is similar to the Sloppy Thomas. Whereas the Sloppy Thomas is generally used to describe peeing in the butt for either heterosexual or homosexual anal sex, the Sloppy Thomma is reserved exclusively for homosexual acts or acts involving beastiality.
My urethra hurts from giving that dude a Sloppy Thomma. OR My dog stopped eating peanut butter after I gave it the Sloppy Thomma.