What I take from this little story is that perhaps someone, a total stranger, got into your personal space and you let it happen. It is a good way to get knifed, robbed, or who knows what.
Situational awareness is the key to survival and I never let anyone violate my personal space. If they attempt to, I have no problem requesting, politely at first, if they wouldn't mind just giving me a little more breathing room. If they do not get the request, I become a little stronger in my wording. I'm 6'2" and tip the scales at 225 lbs. I do know that I am no match for a guy with a knife that is in my face so why put myself in that position?
I live in an affluent area where street beggers are at every stop light. It amazes me that the police allow this but the fact of the matter is it does exist. Even in my car, when I drive with the windows down, I always request the beggers to keep their distance. The very last thing I want to do is have to pull my gun because I allowed someone to enter my personal space thinking he has evil intentions.
May the Schwartz Be With You.