Short and sweet, he would have gone home KNOWING that he was a STUPID IDIOT, what he did was HIS fault, and he WAS going to pay for repair to ALL damages he had caused to ALL of the equipment.....or he WOULD regret it one way or another. Like others have said holding it in over the small crap is kind of expected with family, but for something like this boundries HAVE to be set, a line has to be drawn and he has to know which ones he will not be allowed to cross.
The way you now feel is, obviously a result of having held it in far too many times. Letting yourself get to the point you are ready to "kill" someone is never good. Instead, let it out a bit at a time, when the time calls for it, and in the end everyone will feel much better. That said, just because he has medical training does not mean he isn't a complete idiot when it comes to machinery. He's no more qualified to operate any type of equipment than you are to cut someone's throat and insert a tube to save their lives. If he keeps going like he is, ultimately it will be either his or someone elses life that will need saving due to his stupidity. It's time to stop the madness before things get to that point.