The tan one receives by commonly wearing ridiculously long shorts in the summer. Generally only males are rendered with this strange positioning of tan lines, primarily due to the popularity of basketball shorts which go down to only about six inches from the ground. Since only about half of the calf is exposed to sunlight it's the only part of the leg which becomes tan. When worn in conjunction with equally popular (and equally bogus) over-sized shirts, the resultant tan leaves the appearance of a pasty-white scuba suit worn by the afflicted subject.
Jill and Sally were at the local watering hole.
Jill giggled. "My boyfriend John always wears basketball shorts in the summer, so every fall he winds up with a scubatan."
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.