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I don't think there's anything particularly surprising about the level of rudeness in New York. A lot of it is just show. New York has been portrayed in so many books and movies and stand-up acts that the stock characters know how to behave badly. They've all read their press clippings. The Jewish deli waiter knows what to say to an out-of-towner who asks if he could get a pastrami sandwich ("When I'm ready, I'll get" or "Listen, the pastrami here I wouldn't wish on Arafat"). The Irish cop knows how to act like an Irish cop who does not go overboard in showing respect to the citizenry. Some of the newer stock characters, like the Korean greengrocer and the Indian news dealer, aren't certain how to act yet -- there haven't been enough movies about them -- but when they do get it all hardened into a New York shtick, I rather doubt that they're going to sound like the flight attendant of the month.
Also, I believe rudeness tends to vary in direct proportion to the size of the city, so it's only natural that the largest city is the rudest. It isn't just that the little daily irritations tend to build up in a large city faster than they do in a small town; it's the anonymity. In a small town, what you shout at someone who makes a sudden turn in front of you without a signal is limited in nastiness by the realization that you might find yourself sitting beside that person the next day at the Kiwanis lunch or the PTA meeting. If the town is small enough, the chance that you'll never see the offending party again is nonexistent. That puts a sort of governor on your behavior. In New York, the odds are almost the opposite; you are almost certainly not going to see that person again. The governor is removed. Knowing that, you might do a lot worse than "Ya jerky bastard, ya."
Not you? Yes, you. Right at the top of the list you should write down that there's nothing genetic about any of this. New Yorkers weren't born that way. A lot of New Yorkers weren't even born in New York. Some of them were born on farms. I was born in Kansas City. If you moved to New York, you'd be a New Yorker, and you'd act like a New Yorker. You'd only glance for a moment at the guy costumed as Eleanor of Aquitaine. You'd scheme to get the last seat on the subway car. You'd become a comedian. You might even use harsh language with taxi drivers. You wouldn't behave that way? Well, how about Mother Teresa?