There's really nothing anyone can do about another person losing their cool or doing any other kind of stupid shit, unfortunately. There is no universal or even remotely reliable method of teaching someone how to keep their cool because the change absolutely must originate from within or it simply cannot happen. We can all try, but it's futile if the person that can't control themselves isn't putting forth the effort, can't, or whatever. The best one can do for such people is either leave them be or dismantle their excuses: both of which are equally prone to failure.
Leaving them be is surrendering and discarding your ability to influence them positively: if they can't help themselves, how can you? There's no sense in provoking someone who'll go to blows over the smallest thing and since the smallest thing does set them off, why bother? I mean it's obvious nothing you try is going to help them do anything but get angrier so isn't trying to help them just a detriment to all parties involved?
Dismantling their excuses and crutches for losing control forces people to confront the issue directly. Yes, it's going to piss them off but if they don't look beyond excuses themselves why allow them to get away with hurting themselves in such a way? It's not going to do you any good just allowing that sort of behavior, it's certainly not going to do them any good. Take their crutch right when they're relying on it instead of thinking and break it into a hundred pieces right in front of them. Do not employ subtlety, piss them off with your destruction of their crutch and the weakness it represents. They'll look for another one, break it too. Keep on doing it until they're out of excuses, in their desperate attempt to blame something or someone other than themselves they may even realize that it's their fault alone that they're angry. And if they're not forced into a position where they're thinking about it, how will they ever learn? Obviously they're unwilling to slow down and think for themselves, but in their desperate search for crutches they may employ a modicum of critical thinking and be able to accept responsibility for their own actions finally.
But of course both of those are prone to failure, like I said. Apathy has a low success rate but at least keeps your hands clean, forcing someone to confront their issues can result in violent outbursts or just having them RQ and leave. Peachy, huh? Well these are just my personal favorite tools for dealing with it. There's a myriad of possible solutions people can suggest just as kooky and shortsighted as these that are equally unreliable. It's not some kind of zen philosophy or anything, it just is what it is and change always must come from within. What finally triggers the change is happenstance and ultimately moot in itself.
I can say though that giving people outlets for frustration is basically reinforcement of negative behavior. Stress toys, them finding a way out of the situation that they blame for their loss of control, and the similar sorts. Stress toys reinforce the idea that it's okay to let out frustration in a negative manner(in a subliminal way), allowing an escape will resolve the immediate situation but what happens when they have no escape and must confront it themselves? If they aren't figuring out how to deal with things, giving them a crutch or an escape will be a bad idea in the long term. If they can't figure out how to cool down and stay in control under pressure on their own then they simply won't.
EDIT: And another viable, though more long-term and time-consuming method I like using is to earn the person's trust with a facade of knowledge and friendliness then gradually presenting the issues with their behavior to them in a very graceful manner that gets them to think. It's as likely to fail as any other, but it's very gratifying to make progress that way, lol.
