Was this guy a cop? Was he in a squad or did he have a badge?

If you don't know, next time he confronts you ask him for his badge, if he refuses to show you call 911 and have him arrested for impersonating a cop.

If he is a cop, get his badge number and go downtown and report him.

In my opinion, these don't sound like normal tactics, a real cop woud much rather catch you in the act and arrrest you.