Yeah I have a similar problem with video games, although i've tried to not hurt myself, and I would "hurt" other things like whatever was around me. And I would try to not damage something too much.
The only times I'd ever hurt myself is if I did something wrong, and the other person was mad at me and I was mad too.
Normally what I do is rip up paper. It's been a good way for me to not damage any more things, like staplers. I've broken tons of staplers, pencils, pens, I even threw a chair once, scissors, books. Stuff like that. And when I hurt myself I hit my leg or scratch the sides of my face or my hands. Usually when I scratch my hands they bleed and that's not too good. Then they hurt like crap later.
Like instead of hurting yourself, try "hurting" other things, preferably easily replaceable things.
Yeah and I do the same thing in public or around people. And when I feel I am about to have a meltdown I excuse myself or I just leave and I go to a private place, usually like a bathroom and just meltdown in there and come back. The coming back part is often the most embarrassing, since the people know I went to freak out or whatever. And I have meltdown..ed in front of some people, like my family, a few of my friends. But never around strangers. That would be weird.
Just whenever you feel you are about to go into a meltdown, don't try to calm yourself down, just let it go, but restrain yourself from doing something too severe (like hurting yourself). Maybe try the paper thing, and I know it may sound kind of stupid but it helps. Also if that doesnt work for you (papercuts are my only problem with that) then hit something else, like a pillow or anything to substitute your own self, of course dont hit anyone else but I'm pretty sure you wouldn't or have never done that.
_________________
We could sail on a pancake sail ship in an ocean of chocolate. And if it sinks we could hitch a ride on a ratatouille rocket.