an abbrievation of sucks to be you. this is used when someone else has an fml moment and you really dont feel sorry for them. you actually find it funny, and are glad that it didnt happen to you. stbthem or stbhim/her can also be used.
bob: today i asked a girl out and she rejected me and then i ran into a locker and broke my nose.
jimmy: stbu!! hahahahha
jimmy and bob drive by the school band practicing in the pouring rain.
jimmy/bob: stbthem!
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.