Been in a few. The only one on ones were before high school (when you're generally not going to seriously hurt anyone or get hurt, at least in my time

). The ones I've been involved in since high school were generally to try and break up (or help out in) fights that friends got into. Since graduating college (a long long time ago

) and entering the "real world", I can't say that I've been anywhere near a fist fight.
The best non-fight I've ever been involved in was at a local bar while I was in college. This big 6'4-ish, 250-300 lb-ish guy shoved me out of his way (I was standing in the aisle next to the bar talking to a couple of friends who were seated on barstools at the bar). He must have tossed me about 5-6 feet from where I was standing. Having had a few beers and being a bit more courageous than I should have been, I got up and walked back to where he was standing and told him that if he wanted me to move, all he had to do was ask politely and I would have got out of his way. I then "demanded" an apology. To my surprise (and probably everyone else's), he said he was sorry and didn't know what had gotten into him. He asked if we were cool and I told him "Sure." and he left. Thinking back, I'm not sure if I would've done that again, but it certainly worked out!