As a professional porn "star", I felt the need to add to this:
"Cock monkey" is a variant for male porn star/ legal professional male whore. It addresses the mechanical aspects of prolonged sex for commercial entertainment purposes, in multiple positions and in camera friendly ways which are different than sex in a private setting.
A guy fucking for a living on camera is a cock monkey or porn star, or both, depending on how you look at it.
If, as a porn star, some other dude director is telling you when to get your dick up and when and where to shoot your wad then that makes you a cock monkey. If the director is telling you to raise your ass higher so he can see you fucking the chick doggie style from underneath, that makes you a cock monkey.
You may also consider yourself a porn star at the same time. Being a porn star requires charisma, fame, talent and ego.
Being a cock monkey requires having a dick and being able to perform the most basic duties on command like getting an erection and ejaculating within a small window of time.
No P.h.d. required.
"There sure were a lot of cock monkeys in that gang bang. I could barely see the chick at all with all the dudes surrounding her"
That guy's not a porn star, he's just a cock monkey. He does low paying porn jobs like bukkakes and load dumps after the girl fucks some other guy.