Basically twice.
First was in 3rd grade by a kid that was held back one year. My teacher told my mom that he would always put the two of us together because I stood up for myself better than others would. I was small for my age and more beautiful than any woman so naturally he saw me as an easy target, but it was generally just pestering (knocking my things off the table, calling me a Nazi because of my German heritage, etc) except for one time where he pushed me into a bush and I got scratched a little, but I'd put my best effort at getting back at him even though he was obviously my physical better. My dad was a very strong advocate of "Hit back twice as hard" as well, and got me lifting weights and stuff (not that it likely helped then) though.
Second time was in 6th grade, by this beady-eyed asthmatic little fucker, one of the few kids smaller than me. It was always cowardly passive-aggressive stuff, like using a hollow mechanical pencil as a lead blowpipe (I stood up knocking my table over and yelled "Do that again!" with my history teacher giving a deer-in-headlights expression), or jumping over my head when sitting at my spot in PE (grabbed his leg midair once and he fell face-first), to eventually just laughing at me from a distance. At one point I gave him a bloody nose and told him that I'd shoot him the next time he laughed at me, and I was expelled from school for that.
Expulsion completely killed all my early burgeoning machismo and I just sit back in sullen virginity as all the non-manlets of the world enjoy its riches. In college this one guy just straight-up said "I want to fuck you in the ass! Fuck. You. In. The. Ass." motioning at his own butt, and all I could do was glare at him. Obviously it's probably a good thing that I didn't just blow up on him like I would have as a kid, but the experience of being a cowed pussy afraid of consequences for retaliation is honestly depressing. I spent at least a week stewing in anger over how much I would have liked to see him raped and killed, where taking care of business immediately would have blown off that steam immediately.