From the word 'Gammon' which has negative meanings (such as 'fake', 'bad' or 'stupid'). Gamdog is used to describe an individual who shows one or more of these qualities.
The word has its origins in The Northern Territory of Australia, particularly the capital city of Darwin, where it has evolved from the local pigeon-english group of slang.
"Aye brus! That one bloke over there bin acting Gammon, look."
"yeah true cuz, hes one Gamdog. Lets bitz him jah!"
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.