1) Any time a penis is particularly floppy, such as a few minutes after a good shag session.
2) A lazy person, especially someone who's always on the couch.
3) A pujorative term to describe someting that is floppy or more floppy than it should be.
1)Man, I just shagged Sarah hard for almost two hours, Ive got the worst flopcock Ive ever seen.
2)Ian wont even got off the couch to take a shit, what a flop-cock.
3)Man, those new springs I put in the truck are WAY better, especially after riding around on those old flop-cocks for three years.