One thing that you probably shouldn't do:
When you are alone at night and parallel parking in an unsavory part of the neighborhood and it's a tight space and you do that thing where you ease back until you gently, barely tap the car behind and then when you get out of the car suddenly you realize there is a teenaged white trash couple getting out of their car to come at you and saying "yo bitch, you just hit our car."
What you probably shouldn't do then is say "Yeah? Relax. It's called a bumper."
But if you do: memorize their license plate number, dial 911, and haul ass out of there.