Yes, I was a bit of a bully when I was younger, and then bullied myself. The one that really stands out is a girl who had acne that I would make fun of on the bus probably around 5th or 6th grade. God, I said the most awful stuff. She never broke down or anything and I remember her saying strongly that she didn't care what I said, but I'm sure it hurt. I'm very sorry for doing that and regret it to this day. There were others too, I know there were. I was still relatively popular at that time and would pile on with the others.
At some point I grew distant from all these friends and started to become unpopular or at the very least just kind of fell into the background. At that point I got to experience the other side and I was bullied a bit. I remember being "pantsed" in the hall during passing period in middle school once, that still haunts me. A group of bullies who really tormented some other kids would occasionally threaten me with violence for no reason. Other kids, some who used to be friends, just kind of ignored me. I remember once getting randomly paired up with this girl for a project and she started to cry. No idea why, but that messed with my head. Wasn't too bad compared to some other kids (we had to have an assembly for one of them, because he was suicidal and afraid to come to school...), but Middle School was pretty rough and that's when I became "aware" of how shitty bullying is. I just kept my head down for the most part. I started snowboarding and paintballing with some old friends and that helped.
By high school most of the bullying had stopped. I was still pretty shook up and bitter, but I had some good friends over the years. Unfortunately those experiences really stunted me and I just kind of avoided most social aspects of high school and lived in my own little world. Looking back I realize I was pretty well liked, but those experiences made me distant and stand offish. I know it's just high school, but I regret not making more of an effort at that point, I was (and still am) just very sensitive emotionally.