I spent most of my school years in Kansas, and when I moved to the Wash. DC area in '77, it was like running down the beach into waist-deep water...at least as far as 'public' dealing with people. I joined the Folklore Society, and met many nice people, but cashiers in stores, clerks in offices, drivers, phone answerers, cab drivers...etc., wow! I was amazed at the brusk, impatient, rude and generally 'me first' attitude I met...(with the obvious exceptions).
After a few years I went back to Kansas to visit, wondering if it was my imagination, but for a week, it was like old times....no one cut me off in traffic or ran red lights, and grocery store clerks looked up and said "hello" and clerks at counters noticed me, even if I had to wait a minute for service.
   I have my personal theories about the differences and why they developed, but after driving at various times in over 40 states, I see 'generally' a trend that the larger the metropolitan area, the worse it seems....with Seattle a bit better and NYC a lot worse.