I was, but not in the typical sense and not deliberately. My school had a major bullying problem anyway, so mostly it was attack being a form of defence. And I made a special point of only doing it either one on one or where I was outnumbered. And I was very keen to defend the underdog, anyone I thought was vulnerable I would stand up for. And in any case, the other person had to start it, I'd just finish it.
Admittedly I often took things to extremes, was only ever physical in defence, but verbally I was articulate and vicious, with the ability to rip someone to shreds and make others laugh at the same time.
And from my perspective, anyone who didn't meet my criteria of vulnerable and got upset about my behaviour was pathetic and needed to stop being so weak.
So eg girl x made a comment about y being a thick tramp. I knew y's personal situation and went to town on x immediately, and also her best friend who tried defending their right to insult y. And I continued it for years. When x cried in front of me, and y told me x was frequently upset by me, she sank even lower in my estimation because she clearly was not only a bully herself, but then wanted to play the victim. And whilst I can acknowledge now that lots of what I said and did was worthy of tears, and I could have made my point without being quite so vile, compared to the shit I dealt with all the time as a teen, it was her problem if she was too sheltered and weak to cope with anything a classmate said. Unless there was another complex reason, imo back then anyone who could go crying to mummy over something I said clearly had fuck all to be crying about.
And most of the situations I was involved with were like the above.
On the other hand, a girl dd knew when younger did it because of her pfb parents. She had no concept of anyone else's feelings, and had spent her life thinking anyone who didn't do what she wanted was horrible, and therefore she could be horrible back. And no concept that she wasn't the centre of the universe. School obviously didn't agree so she then went through a phase of doing sly things and then running off crying when the victim retaliated. Unfortunately the pfb parents ruined schools efforts, and at secondary the poor kid has no friends, a victim complex and is still bullying others.