I think, being a guy especially, these sorts of things will happen and there are always times where you feel the desire to punch someone, either in self-defence or because you're pissed off. In all honesty though, you can resolve most things by words. If the other party doesn't agree then obviously do the safe thing and leave, which is what I'd do - don't worry if other people call you a chicken or whatever, it's always safety first, not just your own, but that of others too.
Anyway, even though I've never been involved in a physical fight (I've avoided some by pacifying and I've been punched in the stomach once by this guy when I was in Year 11 - but nothing serious), I've witnessed a fight where someone had to be hospitalised, but this is pretty much a gang thing where tension has been boiling for a while, not a one-on-one kinda thing.