From the hilarious tv cartoon Ren & Stimpy, happy happy joy joy is defined as when the world expects you to put on this happy and joyful face when what you really want to do is shriek at the top of your lungs and rip your hair out in anger/frustration/misery. To make everyone happy though, you put on this mask of happy happy joy joy while singing a silly song.
Just as you were ready to leave work for the day, the boss tells you he wants you to work both Saturday and Sunday on the new project. You're on salary and so will get no more $$ for sacrificing your weekend. However, the boss is considering you for that vacant position where you'd have your own office with a window, so you happy happy joy joy and say, "Sure thing, boss!" with a big toothy grin on your face.
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.