A fat or very ugly chick who causes stiff erections to flop.
Nicole is such a cock flopper no guy could ever keep it up around that slore
A guy who likes to shake his junk a lot. Especially while wearing loose fitting shorts so that their junk makes a slapping noise against their leg. This is often perfomed naked in front of mirrors.
Thelma: I caught Brad shaking his junk in front of the mirror when he got out of the shower.
Beth: OMG! He is such a cock flopper!
female or instance that immediately makes your manhood floppy.
Fat people having sex, road kill, your mom knocking on your door when you're getting a BJ.
Those two slamhogs making out in public is a real Cockflopper.