Phrase describing a person who lacks the collective intelligence of a box of rocks; possibly a bit more intelligent or a bit less intelligent than a person who is dumb as a rock.
John lit a match so he could see where the gas was leaking out; he's dumber than a box of rocks.
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.