When a pimple or boil has been popped manually, but you are pretty certain that it will reappear because it isn't quite done, it is said to be fesculating.
I had this really gross zit on my back, and I popped it yesterday. It still feels kind of sore, so I am sure it is fesculating. It'll probably be twice as big as before tomorrow.
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.