Hey OP, I think you inadvertently invented a new word, and a darn good one at that! There wasn't anything wrong with the gun--just the "man" holding it and pulling the trigger. So, therefore, it was a "manfunction"!
It's easier to blame the inanimate object that to admit on TV, with potentially millions of people watching the original broadcast and all the reruns, that you were a "dumb-A" and had your thumb in front of the muzzle when you pulled the trigger! He wins the "prize".