^^ Umm, basically what he said, except I haven't really hurt my wrists before but I've busted my hands open pretty badly. I've put my foot through chicken wire window and needed several stitches. I punched a project I made in auto shop class hard enough to break welds on it. One of the more common causes of meltdowns when I was in high school was bullying/harassment and often those would lead to blackout rages where I was perfectly fine with the risk of injury although by about grade 11 that ceased to be a likely outcome.
I've gotten very lucky too, when I was 15 I put my hand through a wall four times (first two passed through the front and back drywall). If I was an inch to the left on any of the four I would have busted my hand on a stud.
I've knocked myself out banging my head while dealing with a sinus infection. Self-harm is more likely if there isn't a direct instigator that can be targeted. If there's an external provocateur that can be reached I'm more likely to just get red mist.
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"Many of us like to ask ourselves, What would I do if I was alive during slavery? Or the Jim Crow South? Or apartheid? What would I do if my country was committing genocide?' The answer is, you're doing it. Right now." —Former U.S. Airman (Air Force) Aaron Bushnell