Poop Dick Flakes(PDF) are when you have had anal sex with your penis. After sex, the poop on your penis will dry up. When the poop on your penis dries up, you start losing your boner and the poop wil flake off onto the floor.
"Hey Jeff! That was some great butt bashing. Now come over here and look at my Poop Dick Flakes are falling on the floor!"