From TTAG Commentator Magoo:
Very often, robberies and assaults are not cold calls. The potential perp will first approach you with some pretense — asking for a dollar, for directions, for a ride, etc. This person is some combination of desperate, mentally disturbed, and criminal, and in these first few moments he’s deciding whether he might rob you, or whether or not you are Satan, or that maybe he’d like to kick your ass for the hell of it.
This is how many people get robbed by criminals/attacked by crazy people / both. The victim thinks he is merely trying to extract himself from an awkward social situation, not realizing until it’s too late that the confrontation is about to turn violent. In fact, these first moments are crucial.
First, never engage or argue with these people. Make it totally clear with your voice, actions, and body language that you want no conversation or contact and that you are not a suitable victim. Understanding who you are dealing with will get you out of more situations than a gun ever will.