If I could go back in time, I'd get into more fist-fights. I feel like I missed something, being a boy and never having flat-out decked a bully. But, honestly, I never quite had a reason. I was pretty nerdy in elementary school. I would skip recess most days and go to the library with my nerd-friends to draw, talk about video games, and do other non-physical things. I was on the receiving end of some name-calling, but I had the advantage of being a lot bigger than most of the other kids--a friendly giant, really, but they couldn't be sure of that! So the bullying was unusual.
I do often recall situations that I wish had gone differently, though, whether they're from my early childhood or from yesterday. I think some of us are just more sensitive that way. For example: My parents rarely spanked us, but I can remember a couple of times when I was spanked for something I didn't feel was that bad, and I could start crying even days later just by thinking about it. And we're talking one or two good smacks on the butt, not a beating. Looking back, these were very small things in the context of an otherwise-pampered childhood (sorry), but to get over them took me far longer than the average kid, I think.
When I start to get into a funk about stuff like that, I try to remind myself that nobody else who was involved with those situations is still thinking about them. They've grown up, forgotten, etc.--most of the time. Amusingly, I was contacted a few years ago by a former high school band classmate of mine who I hadn't thought about once in the preceding decade. She asked how I was doing, and then went on to apologize profusely for ousting me from first chair in the oboe section. Talk about weird! (At the time, I found her kinda cute and was just happy to sit next to her!) But clearly she felt she'd offended me, and it had bothered her for years. And after she got it off her chest, I never heard from her again.
Bottom line: We're all a bit strange when it comes to the things we cling to. It sucks to have baggage, but try to assume more of a third-party observer role in those old memories. Often times, one can find a speck of amusement that way.