Firstly, let me say that I realized, long ago, that trying to exhaust every single situation that you could potentially land in will drive you mad. I, therefore, don't lose sleep over "what if" scenarios. Sorry.
Secondly, if a crazy person gets that close to you, then you've most likely fucked up. Use your observational skills and avoid a confrontation. If something doesn't look right, go the opposite direction. When you have a gun, if you are not Armed Security or Law Enforcement, then you should be avoiding situations unless it is CLEAR that your presence is required (example: you observe an armed threat attacking someone, or see a woman get raped behind a dumpster, etc etc).
And remember: not everyone who's hyped on drugs is unarmed. You'd be surprised what a person hyped on drugs can do without a weapon. And anyone who doubts this is either out of touch with reality, or has never spoken to a police officer in a high-crime area who deals with drug users regularly. And, unfortunately, this also applies to the mentally ill. It is ludicrous to think that I should have to treat Joe Crazy any differently because he's mentally ill. They too are perfectly capable of killing people, and they have many times before.
What am I supposed to do if a mentally ill person attacks me? "Oh, well, he's bat shit crazy....can't draw my gun, he's mentally ill"? I don't think so.
It's true that, sometimes, you can't avoid a situation. So let's say, for example, I'm passing an alley way, and some drugged-up loser comes out of there demanding change or something. I decline, and he attacks. If he doesn't have a weapon that I can see, then I'll beat the ever living fuck out of him physically, and look for an escape route.
But if he produces a weapon, all bets are off. My goal then is to get away and get distance, firstly. Secondly, if he continues after me, draw my gun and give him clear instructions. If he doesn't obey those, he gets shot.
It is important to recognize the "Use Of Force Continuum" when dealing with such a situation. Which is why the law says that you can bring deadly force into a conflict where the other party is not immediately armed (note that "Armed" is not the same as being a "Threat"; you can be a threat and not be armed). For me, the only way this would occur is a couple of instances:
-I am outnumbered (for me, that's 2 or more people)
-I am out-sized by the opponent (for me, that's anyone 6 feet or taller with a muscular build. I'm 5-6 and 230 pounds of out-of-shape fat. I'm confident that I can defend myself in a quick fight, but nothing drawn out)
-I am losing a fight (for me, that's being concussed, worn out, battered pretty good, or being subdued by an opponent)
That's just what I can think of off the top of my head. And that also DOES NOT mean that just because, in those situations, you draw your firearm, that means you have to shoot a person. Anyone who thinks that is a fucking moron. In fact, I think the media plays on people's ignorance with that particular subject of self-defense with a firearm. If you are able to draw your gun and issue commands without firing shots (which constitutes "bringing deadly force into a conflict"), then that is a win. Even better if you can get away without anyone getting hurt.
So bottom line if you are going to carry: 1) don't worry about "what if" scenarios. You'll drive yourself mad. 2) ALWAYS be aware of your surroundings. God gave you eyes for a reason. Put your fucking IPhone away and pay attention. 3) Be dilligent with your training and practice. Even if that means going to the range each weekend to practice your marksmanship. 4) Study self-defense laws for your area and State. Talk to people who carry, but listen to the experts. Study experts on Self Defense, such as Massad Ayoob and Clint Smith.
