When you place your mouth upon someone else's anus and proceed to inhale as they shart. Like a shottie, except with a shart.
Bro 1: Yo bro, shit got weird the other night with my girl. she gave me a shartie
Bro 2: A shottie bro?! I didn't know you smoked!
Bro 1: Nah bro I sucked a shart out of her anus
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.