When you rub your belly after fondling your gun collection. Your belly is wet on account of the jizz that comes out of your dick when fingering a barrel hole.
I stuck my finger in the barrel of the gun, and I spontaneously came on my belly. I couldn't stop jiggling my wetbelly.
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.