"You can't hit a girl". Fuck that. If a woman hits a man, a man should be able to hit her with as much force as is necessary to stop her from assaulting the man.
Do you really believe it's okay for a man to hit a woman? I find this hard to believe.
Of course it is. Show me a man who doesn't protect himself and I will show you a weakling.
It's never okay for a man to hit a woman. It's not acceptable for a woman to hit a man either, but a man, in general, can cause a lot more harm. There are other ways to resolve conflict.
If some woman hits me, I will smack her back.
It is okay to back away from the situation to protect yourself, but under no circumstances is it okay to hit a woman as you can really hurt them. Resolve your arguments with words not fists.