Well, this seems very much like a MADE UP WORD, cooked up by the strange imagination of this Alex person, but if you're gonna be making up words, at least make them a little more plausible - spaghag sounds much more like it would stand for SPANISH FAGHAG.
You're such a spaghag, "man". (In keeping with Alex'srubbishexamples)
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.