This is a variety of teenage/adolescent female who tries to gain favored status with teenage males by always sitting on their lap. They also like to sit on the laps of older men to gain the same status.
Hey Son, tellKelly to stop sitting on everyone's lap around here like a Crotchmonkey.
Jim: Hey Bob, let's go to Chotchky's for lunch.
Bob: Sure, sounds great!
Larry: Where we going guys?
Jim: Don't be a crotch monkey, you're not invited.
-A human of Neanderthal-like mental capacity with a strongnatural proclivity toward Dickdom
"Listen, you ignorant crotchmonkoid... shut the fuck up and go back to making cave-paintings of Bam-Bam fisting Pebbles before I kick you in the spine."
an abnormaly large bush, which hangs out of underwear or even a pair of shorts, typically looks like the person has a baby monkey hiding in their underwear
guy one: did you see how amanda was sitting on the picnic table
guy two: how could i miss it? was she trying to show off her goods to everyone?
guy one: goods? more like BADS! that girls got a crotch monkey guy two: oh god, dont remind me
guy one: should we get her some napalm for christmas ?