yes, ma-ai and constant vigilance etc... but
the Chinese martial arts have a saying that I don't remember exactly, something to the effect that "anyone can make themselves unbeatable but that to do it you have to make yourself into a savage beast"
ie: Samurai from the warring states period (or even the stories about Sokaku Takeda) who basically considered anyone within a few feet of them as possible enemies, especially any groups. never relaxing garde, always being armed and even sleeping with weapons, etc... living as if in a mortal threat situation at all times.
most of us wouldn't want to, and probably don't need to, live with that consciousness. but in threatening situations it's something to remember re the ma-ai. if their standing where they can touch you then you're in active danger.
*there's a self defense program (http://www.rmcat.com/
) that demonstrates exactly this attack (they describe it on their website) . the instructor with a concealed practice knife starts talking pleasantly to the group and moves close to someone, puts his hand on their shoulder, and suddenly pulls the knife out stabs several times
and a very interesting self defense site (not "how to" techniques is http://www.nononsenseselfdefense.com/
here's a quote
"Let's start with the fact that the self defense defense is an affirmative defense.
Go back and read that again, it's important. An affirmative defense means, by claiming self-defense, you are coming out and saying "I did it."
Specifically, you are admitting to actions that are normally a crime.
Read that again, you're admitting to what is 99% of the time, a crime. But, you are saying that you did those actions in order to stop the same criminal act from being unjustly done to you.
Once you claim 'self-defense' you can't go back and say "Well, I didn't mean that" when -- and if -- things start going badly for you. You've confessed already. Even if it started as self-defense, if you crossed the line, you've just plead guilty to it.
Let's add another term to your legal repertoire: Burden of Proof
By using the self-defense defense, the responsibility of proof is on you! You're no longer innocent proven guilty! By confessing, you're guilty until YOU can demonstrate differently! YOU have to PROVE that what you did was not only self-defense, but justified. It isn't self-defense just because you say it was (Remember both sides in a fight claiming it was 'self defense?'). So right off the bat, you're going to have some explaining to do.
This is why it is important to know where your actions stop being self-defense and turn you into an aggressor. If, upon investigation, it is found that you crossed the line from self-defense into assault, you've confessed to that too."