all shapes and stripes

Bullies come in all shapes, sizes, colors, genders, and religious affiliations. I have experienced people trying to push me down who were females in my life; people who were much shorter than me and taller than me; people who were supposed to be leaders or teachers of faith; people who had or were working on more advanced degrees than I had and people who have had less education, too. I think I must have an invisible sign on my forehead that says "Bully me, please. I won't care." Nah. The reality is that bullies are just insecure or mean people who think they have some advantage over me or you and try to use it against us.
I believe anytime we use a supposed or real advantage we have over someone to gain power, gain pleasure, manipulate, hurt, belittle, or use someone for our purposes, and to their detriment (hopefully that is obvious), we are acting the bully. They might even consent to it. That does not matter because the advantage we think we have nullifies their willingness to submit as being free choice.
During junior high and less so in high school, a guy I knew attempted to be a bully to me, even though he was by the end a good 6 to 8 inches shorter than I was. But he was mean, and brash, and thought that because he had the "right" friends, he could get away with hurting or belittling me. The older I got, the less he did it. I think he at first thought I was a dork from a wealthy family who needed picking on, who maybe curried too much favor with teachers and maybe was too nice or naive. But as time went on and I grew taller, and he didn't, as I proved I was a good athlete, and he was adequate, and as we grew less entangled in terms of not really being in the same classes or spending much time together, his bullying decreased. And I probably had tried to do some things initially to get on his good side or be his friend; maybe he took that into account.
So, size doesn't matter. The saying goes something like this: "It's not the size of the dog in the fight that matters, it's the size of the fight in the dog." This guy had a lot of fight in him, and maybe due to his brothers picking on him and having to find a way to survive. I am sure that is at least partly where he learned it. It doesn't make it right. But beware, just because I guy is small does not mean he won't punch you in the nose.