When you are having anal sex with a girl and you pull out and put it into her vagina.
Friend #1: I was have amazing anal sex with that filthy little filly Stacy and I pulled it out and put it deep in her bum, straight mud-flappin' bro.
Friend #2: Amazing, pure class.
When your having sex doggystyle and the girl explosive diarrheas on the man's testicles.
"Did you hear what happened to Josh? Melissa gave him a West Virginia Mud Flap"
The act of smearing shit all over yourself and your partner. Then sliding all around the bathtub together
Babe I have had a long day can. So please can we have a Florida Mud Slide.
The act of anal sex that is excessively messy
Ted went mud Spilunking with Jen after taco Tuesday.