Seems like I'm the only guy in this thread who actually fitted the normal definition of "bully" then...
Well, here goes:
When I was about 10, I was right at the top of the social ladder in school. I was lucky enough to be best friends with some of the biggest kids in the year, and combined with getting the best grades, this made me very pseudo-popular. Our little four person group essentially led the school in everything as a result, be it academics, sport or whatever.
Now there was another kid, who we'll call Jim, who was never part of our group. One day he starts hanging around with us anyway, and we all respond in a very hostile way - verbally at first, and eventually spilling over into physical violence. I don't have a fucking clue what our problem was, I honestly don't, but we treated that kid like shit for a whole year. I always used to assuage any guilt I had by saying that I had never physically touched him, which was true, but I couldn't deny myself the depth of psychological damage we did to him.
I remember on the day that the 11 year old kids were leaving for their new schools, he hung out with them and tried to taunt us saying he "had new friends now". I remember laughing at that, because I knew they would be gone in a day.
Looking back at things like that make me genuinely wonder if I'm a psychopath or if I've got some total lack of empathy or if I'm just a cunt. The thing is, I'm absolutely the nicest person you could hope to meet otherwise; in my high school now I'm genuinely popular due to being known as "the friendly guy", and I make an active effort to stop bullying and make people feel included and yet the things I've done in my past make it all feel so vapid. But anyway, back to the actual story. Once our final year of primary school began, he began to fight back. He came out with some racist insults (I'm not white) which I can completely understand his use of now, but at the time I used them as justification for ramping up my dislike for him.
One day, he just didn't come into school.
The teachers finally decided to do something, and it was weird for them because I was essentially their model student, who it now turned out was a bitch ass little bully. Their punishment for us was pretty much non-existent, and the year finished without incident. We both ended up going to the same high school, but we never talked much. Nowadays, we make conversation easily and there's a general sense of friendliness.
Every night before I go to sleep, I hate myself for what I did. I'm too much of pussy to apologise to him; its something we haven't mentioned for years to each other. Equally, some people began to bring it up in high school, shocked that the school's "funny, friendly guy" could have had such a twisted past. And when it did come up, I just denied it, and of course, everyone believed me. The first time that happened, I tried to kill myself. I don't even have the guts to do that as I feel like I'd be putting a death on some kids conscience, however little he actually cares about me.
This was long and rambling, so I'm sorry if it doesn't make much sense. If you've read this and decided you hate me, I accept that. You will never be able to hate me as much as I hate myself.
I hope I answered your question.