When you passionately stare and then wink at another's genitalia. It is typically a sign of flirtation, but has been commonly used in popular culture as a jest.
As I whipped my head back up while kneeling to tie my shoelaces, Richard's crotch was directly in my line of sight. I then continued to stare at his bulge. It was getting larger by the second. I made sure he was looking, and then gave his meaty sausage a kinky wink. If he doesn't know that I want his hairy penis inside me now -- he never will.
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.