When someone is sitting upright and keeps falling asleep. When their head bobs down and they jerk it back up, it looks like they're giving head. Bobbin for cock.
Joe must have been out late last night, because today in World History he was bobbin for cock.
When you or someone is so tired you keep falling asleep over and over causing a "bobbing" effect with your head (with your mouth open). This occurs mostly in the sitting position, and resembles the motions of giving a blowjob.
The act of bobbing your head up and down (almost sleeping) during a boring safety brief that is being given by a pussy officer. This usually occurs right before you get libbo.
pete: Check out that guy.
tom: Which on?
pete: the guy bobbing for cock...must of had too many drinks last night.
It is said of the situation where a person has the bad luck to make contact with his testicles against an undefined surface or object, intentioned or not.
Given the nature of the word, it is more appropriate to design cases where the interaction is made with a moving object, for example, a ball.
Although it is extremely painful for the victim, it tends to be considerably funny to people who witness it.
Today in the baseball game the pitcher took a nutshot; the baseball hit him in the nuts.
Man, I just watched the funniest nutshot video ever.