if I consider someone a true threat to me, I'm going to shoot them, not hit them.
That's just sick. That's not a stance that makes you look like a reasonable human being. At that point you'd be a murderer and you deserve jail.
The first step in these kinds of situations is always to try to keep your head clear and not get sucked into the violence. Try to talk your way out of the situation, repeat to the assailant that you have no interest in fist fights or attacking the person, that you just want to continue doing whatever you were doing and leave things be. Keep your distance if the person tries to get closer and keep trying to reason with him or her. Some macho assholes might try to provoke you by being all "why you being such a sissy bitch, fight like a man", but you shouldn't let that get to you, try to not get mad at any of the insults that the throw at you, they are just words and do not make it ok to attack a person.
The second step is to just simply trying to leave the situation behind, if possible. If it's a party/bar, just leave. I doubt you'd miss anything super awesome that night by calling it a quit at that point. Even if the assailant has hit one of your friends or something, if the situation has calmed down enough so that no one is actively fighting someone and there's just some shit talking going on at that moment, just pick up your friend and leave.
The third step will happen if the person still acts aggressively, doesn't let you leave (either blocks your way out of a room/building/whatever or starts following you around) and there's some shoving & maybe even a few tries to hit you. Try to evade the hits (since getting hit is painful and might not help keeping a level head in the situation) and find a way to restrain them, if the assailant isn't bigger than you.
The fourth step is probably the one where fists will fly and hits will happen. If he/she is hitting you, then you might want to have one final "I don't want to fight you" attempt, but then, yeah, it's ok to not just take it all without trying to protect/defend yourself.
This has helped me get through all threatening situations without more than some shoving around instead of going for the stupid and taking out your gun or some other shit, excluding this one time when three people attacked me all at once, but in that situation one of the guys is a total lunatic, I heard he's beaten people with metal pipes later on (luckily we were just teenagers at that point and no weapons were used).
Remember, defense != physical violence immediately, the best defense is the kind where no one gets hurt.