We're doing this again?
I live in Bethesda, and I've lived in many places in many countries. I am Parisian by birth. Paris is the city I like to call the rudest place on Earth
People learn not to be too polite in big crowded cities - it's a protective envelope you place on yourself when you go out of your apartment, to deal with the noise and jostling and people asking you for stuff.
But in wealthy suburbs or city districts specifically, I think it's not that people are ruder than elsewhere, it's that you are on alert for signs of exclusion, due to your own insecurity.