A "Thousand Mile Smile" is the smile you get when you are really high. It just happens, and it makes you look so stupid. Everyone around you will make fun of you for it. It will begin to hurt your cheeks after a while, but don't fight it. It's part of the fun.
A method used by London gangsters to scar up their victims. A cut is made at the edge of both sides of the mouth then the victim is kicked in the groin very hard. As he screams the flesh on both cheeks are ripped apart leaving terrible scaring.
I wish some would give George W Bush a five mile smile.
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.