I have heard of someone in that situation taking their weapon out and laying it on their lap so the guy yelling at the window sees it and leaves. It worked. I'm not sure I would do that, either.
I'm lucky in that I live across the street from the police station...911 and "I'm on my way"!
Never had to do it, but it's my plan and what I've taught my daughter. Actually, anyone who knows the area wouldn't follow me into the parking lot 
One time I got to feeling like I was being followed, so instead of heading to the house, I drove down the next street where a police officer lives, he drives his police car home, as we got to his house I slowed down and acted like I was pulling in behind his car, the car following me sped up and pulled around me like a shotgun 
I drove around the block home