When a person from the BAY AREA finds a situation, person, or something outrageously funny, it CAN be described by this term.
At a party, a bunch of people are chattering about until they mention a really funny person they all know. One of them then says, "You know Steven? That guy's hellarious!!"
"Man when that girl didn't know what OJ meant, that was hellarious!!"
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.