I punch myself, often in the face. My dad used to hit me when I was younger, so maybe it comes from there.
I usually do it alone, but I've done it on the phone with my dad during heated conversations, and I've done it twice in front of people in desperately miserable situations: once, when a guy broke up with me; and once, when a person who I thought was going to hire me for my dream job, actually told me that he never wanted to work with me and never to speak to him again.
It usually happens when I feel extreme despair and anguish, as well as a burning need to express that pain on the outside, somehow. The last time I hit myself, my face hurt for about a week, and not going to lie, the bruising and pain felt comforting in a weird way, like, feeling temporarily in control.
I haven't done it in about a month and a half, but I'm dreading another big emotional hit soon, and it's not unlikely that I'll be tempted to do it again. I have had moments in the past few weeks where I've curled up my hands in a fist, as though my body is anticipating needing to do it.
Interestingly, I've also made art of myself punching myself, using a jailbroken AI. I got it to generate animations and had it write abusive statements about how I deserve it and worse. Again, not the healthiest probably, but maybe better than actually hitting myself. I wish I didn't have the urge at all, though.