You might wash your car armed but you weren't planning to wash your car, at that moment. You're doing it, at that moment, specifically because there's a car parked outside. Same action, different reason. The point is intimidation, not a clean car.
Also, when did this car become "suspicious"? It started out "strange", which is to say "unknown".
What do I do when an "unknown" car stops in front of my house? Nothing.
Absent some exigent circumstance, why should I do anything?
I now live in a small village (a few hundred people), I used to live in a larger village (couple thousand), before that, in the country with a few neighbors, before that, in a city of about 15,000. In all cases, an "unknown" car stopping elicits no response from me whatsoever.