When I was 13 I was undersized. Diane F$%** (14 or 15 and big and tough - you know the type - bad skin - week old eyeliner still on the face) used to follow me around the school and kick my bag or push me. I was too scared to do anything because if I started something I was sure she would beat the crap out of me. This went on for weeks.
One day, I was so sick of it, I thought to hell with it and I pushed her back. I winced and waited for the beating that was sure to come. It didn't; she just walked away and never bothered me again.
I still don't really understand what happened. Maybe she would have been embarrassed if we had got into real biffo, and she had copped a beauty from me. Maybe she needed someone smaller to stand up to her.