It's never okay to hit a woman.
Reported.
It's ok to hit anyone in self defense. You can't on the one hand aggressively attack someone and then on the other hand claim it is wrong for someone else to hit back and defend themselves just because the person attacking is supposed to be of the gentler gender. You can't attack someone AND claim that you are a gentle person at the same time. The two are mutually exclusive. You can however hit in self defense and still be a gentle individual. Everyone has a right to self defense. The idea that a woman could hit someone because of their gender without retaliation is just like that South African guy in Lethal Weapon 2 who shot Riggs and then dropped his gun and claimed "diplomatic immunity".
No one has the right to just attack others with total impunity, whether it be because of their race, gender, or economic status. Justice should be blind.
Chris Brown's violence towards women isn't self defense. It is more like "You didn't do this that I wanted you to do,or you question how I do things, or you said this in public, now I'm gonna smack you down." That is always wrong.
Of course, it wasn't always seen as wrong, as when men would beat women with clubs and carry them off to rape them, and that was normal.
I'm all for fairness and justice, but that doesn't mean that the door should swing completely the other way and allow women to abuse men with impunity just because they are women...