The fight I got into in the 6th grade, which I lost spectacularly, is what set me on the martial arts road. Went down to the chain tae kwon do(rk) school 2 days after, they taught me some stuff, and the next time someone picked a fight with me, I was ready to throw down.
.. After I extracted myself from the trash can, I realized that the crap national chain karate schools teach really doesn't apply much in a real fight where there isn't a referee, and there aren't any rules. So I joined instead a mixed martial arts dojo headed up by a former SEAL who pulled in techniques from primarily ryuku kenpo, kali, muay thai, and western boxing.
I kept a low profile in school so it was my freshman year before someone decided to pick a fight again, trying to grab my hand and force it into a belt sander in industrial tech. He ended up with a broken rib, two black eyes, a nosebleed, and a limp that lasted for nearly two weeks. After that, I kind of had the reputation as "that nut who'll flip out on you if you mess with him," and no one tried to fight me anymore.
I stay out of the unsavory parts of town, except when work forces me there (and trust me, don't ever attack a photog. Our tripods weigh about 20 pounds, and we're usually in a bad mood when we're shooting on the street
) so I haven't gotten into any physical confrontations since.