The expression "Boys can't hit girls" seems to engender a view that females are, on an absolute level, completely inferior and incapable of defending themselves. Of course I realize domestic violence and rape abound, and they're nothing short of revolting. But why is it so much less revolting when boys or men hurt each other? The expression "Boys can't hit girls" connotes, in an automatic way, that there is something more okay about boys hitting each other than there is about boys hitting girls.
I can't accept it being even the slightest bit of "okay," because some boys are clearly still defying the popular playground rules and hitting girls in the grown-ups' sandbox.
Perhaps it was an act of enlightened, feminist aggression, and he figured, "If I can hit a boy, why not a girl?"
Had he said that, I think I might have told him he had a valid point. Because, if you're of the mindset to enter the ring in the first place, you're going to step up and dance; a vagina's not going to stop you.