Dirty Paintbrush

When a man has anal sex with a woman, then uses the remaining excrement on his dick to paint on the woman's back.

Clarke: I brought Suz over last week and we got a little frisky.

JP: What'd you guys do?
Clarke: Well, I fucked her in the ass, then used the leftover shit on my dick to paint on her back. We called it the dirty paintbrush.
JP: That's fucking disgusting