1. I think hitting a girl in the same instances I'd hit a guy is perfectly acceptable. Those situations include great bodily harm or things that can potentially leave scars, like a punch to the nose(can WRECK your face).
2. I don't understand the where words cross into the physical realm, unless you attack me or my valuables(I will defend things like my laptop that I can't afford to replace), I'm not gonna touch you, the risk of me getting in trouble is too great. I don't care what you say, if you are the kind that says nasty evil shit, you will only have the chance once, I'll be gone before the next chance arises. I don't see how anyone gets talked into punching someone, learn to fucking control yourself, or at least pick better people to be around.
3. Touching =/= hitting. If I was assaulted in a fashion that prevented escape and threatened great harm, I'd jab a mofo in the throat. But up until that point, armlocks and pushing are fully suitable. I can lift a person 300 pounds, I can take him off his feet and lay him out mostly unharmed, unless I positively have to waste him(really REALLY unlikely) I won't be punching or kicking anyone.
4. Bill Burr puts a funny spin on it, although I have seen real cases of what he is talking about.
http://www.youtube.com/watch?v=5W4J6pGkUBo