Yes many times.
I never start fights, but I don't back down from bullies or assholes either.
I've also never lost.
Being a poor white kid who moved a lot and went to new schools every other year or so and usually living in inner city schools where I am the minority, I had plenty of resistance at first and many taunters.
Usually it took one fight where I would stomp on some guy and/or seeing that I can play football/basketball/run track/etc for me to get respected.
These were all fights while in Kinder through High school. I have had one fight outside of school that was at a friends New Year's party. Basically, we had a fun house party going and I brought my older cousin, his girlfriend, and his 15 year old brother.
This other high shcooler party across the street (it was a small neighborhood) ended and a few of these older kids came over to the house where we were at. One kid was about 6'2" and a full on beast of a young man. He came over with a few buddies for only one real purpose, to start a fight. As he was passing through the kitchen he shoulder slammed my 15 year old cousin who was easily half his size in every way and proceeded to stare him down. I immediately moved between them and shoved goliath back saying "what the fuck is wrong with you, step up to someone your own size!" Granted, I'm 5'10" and while I was not overweight, like now, I was no where near his physical size.
My friend, the house owner, also stepped in and told him to calm down if he intended on staying at the party. They guy smiled and backed down and he and his friends walked out to the back yard. There they huddled in a circle obviously talking about us. We immediately said to each other that they need to leave as they will only start trouble. So, one friend immediately said ok, I'll tell them and walked over to their circle. We couldn't hear, but he said he told them they needed to leave and goliath said FU... that's when we saw my buddy just hit the guy in the jaw causing him to step back a bit. Then the fight was on. (found out later that Goliath called this guy a pussy when he walked over to their party just to check out the 17/18 year old chics, so he kinda wanted to hit him anyways)
That friend and a few others of mine all started fighting these other kids and immediately Goliath is charging me like a rhino. He lunges with a punch that I dodge and he hits the wall behind me. I step back and he punches again missing as I duck, this time I shove him away from the patio to a 4' high wall that had a 6' drop on the other side to a lower house. As I do this he grabs me in a head lock and I start wailing on his nuts like they are a pinata. After about the 5 or 6 hit I feel his body loosen up, probably too much pain and lost all strength. I start to pick him up to throw him over the wall when one of my other buddies throws him on the ground. Obviously thinking I was in trouble, little did he know. I then jumped on goliath and proceeded to beat the shit out of his head a few times. I then stopped as he was out and bloody.
Two of his buddies came over and basically dragged him away. Brawl pretty much ended them with all of his friends leaving while shouting threats.
That was the last physical confrontation I had about .. man, well over 10 years ago in my early 20's. Had some great sex that night too. Wife was all crazy about seeing me in action lol.