Is it ever ok for a man

I don't discriminate. If you want to step up and pretend you're Mike Tyson, I will Holyfield your ass.
 
I have let women hit me without hitting back. No matter how angry I get, I just don't think I ever would.
 
Indeed.

And by "self defense", I mean "imminent danger to your life", not "she started it!"

If a girl punched me in the face, you can be damn sure she'd get hit back. Most punches aren't going to kill you, so you're saying you'd allow a woman to physically assault you without repercussions?
 
As a woman I have to say that if I hit a man he has every right to hit me back...which is a damned good reason to be careful who I hit. :p