I was also one of the chubby kids bullied in grade school & junior high. But under the chub was a lot of strength as well. My parents knew I was a strong kid. So they really pushed me to not be physical. We had just moved to the US from Brazil, and so I was also the foreign kid. Needless to say, I got picked on a lot. We tried going through the school's administration, but when one of the bullies is the principal's nephew..... Yeah.
So finally, my parents and I had a meeting with the principal. I sat there, rather stunned, at what my Dad had to say to the principal. Hell, I wasn't aware that he knew half of what I'd been going through, but he knew just about all of it. And he laid it on the line to the principal. "We've taught our son that to respond physically to these taunts and bullying isn't the right course. We taught him that the proper behavior is to bring it to our attention and to the attention of the school administration. But you've chosen to ignore his complaints, and our complaints. So we're now telling him that he is no longer to not fight back." He then turned to me and said, "You're not to start the fight. You're not to respond physically to verbal taunts. But if they touch you, you are to defend yourself." We then stood up and left the room, with the principal's jaw still sitting on his desk.
Sure enough, the principal's nephew was the first one to test this new theory. He came up, started with verbal taunts, then started pushing me. I gave him one solid punch to the solar plexus, knocking the wind out of him. Then I walked away, leaving him gasping on the floor trying to catch his breath.
Unfortunately for him, he did it in front of witnesses, too. Half the class saw him get knocked to the ground by one punch.
Guess which bully I never had a problem with again?
But my favorite was a year later, my last year at that school. Different bully, locker room after gym class. We're all changing, and one of the punks decided to start pushing me around for some reason. He got 3 or 4 solid pushes in, then I turned around with a 180 degree roundhouse punch. It was just a full body swing, no aim really, but I clobbered him in the ear, sending him sprawling into one of the urinals. I started to advance on him, at which point he started begging me not to hit him again. So I stopped, turned around, and started walking away. At which point he jumped on my back. BAD idea, considering I'd had a few years of judo as a kid. I reached over my shoulders, grabbed *his* shoulder, and pitched my body forward at the waist while pulling his shoulders. I'm pretty sure that as he was upside down in the air over my head, he realized that he'd made a big mistake. That impression proved itself correct as he landed flat on his back on the tile floor. He didn't get up for a while.