Self explanatory. Slapping someone in the face with a sandwich. The larger the sandwich, the better. Subs are preferred. For a cheap, tasty slap, head on over to Subway for a $5 foot long.
A double onehanded slap to the face with an open hand. You administer it in on motion, first forehand and then a backhand. It has to be two slaps, hence the sandwich.
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.