Give him a wide birth and you may just manage to hit the old lady with the walking stick you didn't see in your excitment at seeing a nice car parked somewhere it shouldn't be ,
When you say "acting oddly behind my car" can you please explain in more detail? If you are concerned always pull up and call the police; that or drive to a police station, petrol station or supermarket. Do not be tempted to confront anyone, just pretend you haven't noticed them and go straight to security personnel.
he is crazy car man! he is baaaaaad