The shaft of a mans penis is solid like a shaft of steel, but the head of it is soft like a ripe satsuma. Making it bobble about like a bobble head for your car.
"Hi Chantel how did your date with Ian go?". "It was all going great till we went back to his and he pulled out his bobble head cock!"
A person who "bobbles" the cock whilst performing felatio, making for an awkward moment during the sexual experience. This usually involves the penis popping out of the mouth and the giver of the blow job having to awkwardly re-establish the rhythm of the blow job.
The blow job was okay, but Amanda is such a cockbobbler because she gets so into it.
Someone who normally considers themselves heterosexual, yet when under the influence of distilled spirits (and sometimes boosted by cocaine) occasionally find themselves with a mouthful of cock.
"That Barney is always getting lucky with the ladies, but I heard that if you get him tatored enough, he turns into a vodka induced cockgobbler!"