A hot charlie is anything you want it to be. Because of the way it sounds, most people (especially girlfriends) associate it with something sexual (i.e. Dirty Sanchez). Simply ask for a hot charlie, and the other person must determine what his/her definition of it actually is.
Me: Hey, I'm going to ask my girlfriend if she wants to give me a hot charlie tomorrownight after the movies.
Friend: What the crap is a hot charlie?
Me: Oh, I think you know.
Friend: Does it involve an indian burn on the thigh?
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.