As an adult, no. (Since 18 that is, and I'm only 23)
As a teen only about a few times, and those weren't really fistfights, more like me losing my temper at a joke gone too far and lashing out with a single punch that wasn't reciprocated before we were pulled away from each other. I apologize almost immediately afterward... after cooling down that is. I have a very weird sort of temper. I do not get mad at most stuff that would make other people angry. I have a sort of Temper bank. LOL. When people insult me I add to it unconsciously, when they do something nice I subtract from it. When they finally have enough 'bad points', the last insult will be the straw that breaks the camel's back. And I unleash a kind of anger that is very very hard to control. I have to consciously go somewhere else and pant all the anger out before I could lose the urge to make him hurt really bad. ;d I'm scared even of what I can do in those circumstances, not only to the other guy but to myself.
As a kid - LOTS. Not only fistfights, but biting, kicking, and swinging heavy objects at people.
LOL. I was a favorite target for older antagonizers and several 'rivals' (not quite bullies, more like archenemies), because I did hilarious things when I'm really angry.
-Chasing the entire Grade 1 class with a chair when I realized that my nanny left me in the school (first day). Then climbing up a star apple tree and refusing to come down until my nanny or my parents come and get me, much to the consternation of the teachers. Yes I was sorta spoiled, and I was used to always having my younger brother with me. That was the first time we got separated in school (he was still in Kindergarten and in another school).
-Biting a classmate on the shoulder until he bled. I forgot the reason, but he was one of my archenemies.
-An all-out fistfight with an arrogant teacher's pet SOB (a kind of evil class clown more like, making teachers laugh at the expense of his classmates). I was reading a book in the middle of the school intramurals and minding my own business. He saw me and started to pick on me about being a 'nerd' and a 'bookworm' and wanting to impress the teachers with my reading a book in the middle of watching a kickball match (which was boring). I think I won that too. ;D
-A berserker phase with older students. An older kid (waaay older, I was in elementary, he was a junior or senior high school student) would not stop picking on me. Got so mad I chased him around with a beam. Cornering him at a window, I swung it so hard it splintered on the sill, he managed to duck the blow though. That was when I realized that although I very very rarely get mad, and it takes a lot of shit before I do get mad, I really could not control myself when I do.