What doctrine of law allows a man to hit another man who "gets in his face"?

None. It is assault.

In some jurisdictions, you can argue 'provocation' and receive a reduced sentence; it has to be something that anyone would feel provoked by, though, and your reaction has to be immediate -a 'heat of the moment' type deal.

If the person hits you back, generally you won't be charged as you'd both be charged -it's a fight, and generally in that situation neither party wants to press charges as they'd be charged as well. (Though, in some places it doesn't matter, they don't actually need your co-operation to press charges.)

It is assault, There is no law that allows you to beat on someone just because they piss you off. No man or woman is allowed to hit another person without charges being filed by the police. Even if the victim doesn't want press charges.

I suppose this question is directed at me.

Seriously, have you ever seen a barroom brawl between two men that ended in an arrest?

Besides, the implication of my original question was that women get belligerent and in a man's face (especially in nighttime venues) knowing full well that men are unable to even respond in kind verbally. Women even strike men knowing full well that the only recourse a man has is to slink away.

Dozens of such videos on YouTube.

Self defense laws. Anyone who is being, or feels threatened in any way, shape and form may physically defend, protect or force a threatening person out of their own invisible emotional lines and boundaries regarding mental space and personal safety.

you're kidding, right?

You really need to spend a day as a man. You have no idea...

First off, you run the risk of getting the floor MOPPED with your face. Broken nose, loss of teeth, concussions, etc. And then, as the crowd gathers and cheers your pummeling, some jackass is uploading the video to YouTube.

If your cellphone hasn't been destroyed in the melee, and you call the police, they may or may not arrest him, and he may or may not spend the evening in jail, You however, WILL spend the next few hours at the precinct (or in the hospital, filling out paperwork after your reconstructive surgery), and the District attorney will ultimately drop the case because they have a boatload of REAL crimes on the docket.

Stop living in theory, and take a stroll through reality one of these days.

It's the same law that states you can smack your girlfriend (or any woman) for disrespecting you, and means you can punch her to the floor for slapping you.

It is the primitive law of the Neanderthal man.

Disrespecting a guy is really, really bad apparently.