Headclicker or Head Clicker is used to describe someone who is very good at landing headshots in shooter-type video games. Someone who clicks heads, and lands headshots.
Jerry: Jesus Christ, that guy can't stop landing headshots!
Mikey: He's nuts man, that guy is a professional Headclicker.
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.