1. The act of masturbating (the bumping of the tip of the penis) and fist pumping at the same time. This act is usually done when watching exciting porn or when someone just really likes Jersey Shore.
2. The act of making the previous definition motions as a dance.
1. Person X: Dude you wanna go down town tonight?
Person Y: Na I rented a gang bang porn and I think I'm going to cheer on the guys by doing the Head Bump, Fist Pump.
2. Person X: How are you banging a different girl every other week?
Person Y: I just Head Bump, Fist Pump like a champ at the clubs.
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.