I hurt myself when i make a mistake
Be it accidentally saying something wrong or letting something fall from a shelf, I can hardly take it knowing I let something wrong happen. For the slightest things I hit myself; usually a few strikes to the jaw, forehead, or chest area.
I remember at some point in my life I tried living by a weird rule I made for myself: "When nobody is around to punish you for your wrongdoings, take it upon yourself."
Not that I was abused or anything of the sort; My parents did a wonderful job raising me.
In a way, I suppose the physical pain serves as a distraction from "mental pain", as I would call it.