When I got my CCW the instructor was a retired cop and he told us that avoidance was king and then he offered us a truly unique way to prevent a problem before it starts. This was it:
If you see someone who causes you any concern or worries, do this simple thing: look them in the eye and raise your hand high with palm out and fingers spread, just like you were greeting a friend. But then push it away from your body like you were telling someone to stop, and leave it there. At the same time say VERY LOUDLY, "Hey, how you doing, good to see you again" and keep looking at them. They will either look at you with anger because you foiled their attack or they will look at you like they think you've just lost your mind. All you have to do now is say "Sorry, I mixed you up with someone else" and go on your way. Think about what you did:
1) You took away the element of surprise--you know they are there.
2) Everyone within hearing turned at looked to see why you were yelling.
3) You not so subtly told the suspect to stop with your gesture.
4) You alerted them you were not an easy target, maybe they should look for someone else.
He made us practice on him and he said he had people who could NOT do it. They were just too nice and timid to do it in public.
He encouraged each of us to make it a routine part of our lives so it came naturally and easily. I thought it was a brilliant idea!