A piece of toilet paper inserted between ones butt cheeks to keep sweat and/or crap stains from reaching ones underwear
Butt Rag (aka ass tampon). After taking a dump and wiping clean, you tear off 2 to 3 squares of toilet paper, fold them on top of each other to form a square, then fold that in half, then (optional) you apply some baby or talcum powder to the outer edge. Then wedge it between your ass cheeks in the crack. Keeps your underwear nice and skid free until the next dump.
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.