It's probably not as bad as they make it out to be in the movies, but it's far from the most polite place you can visit.
If you are blocking the subway door with your luggage during rush hour, the normally civilized people may become rude. If you catch that same person on a weekend and ask him for directions, he's probably more willing to help. New Yorkers also don't say make eye contact, greet or make idle banter with strangers. And if someone bumps into you, check your pockets to see if you've been robbed; don't expect a "sorry". And I wouldn't trust the guy selling watches on the street to help me take a picture.
halik - It is rude to put a wet umbrella on a subway seat. Especially in a crowded car. So I can understand if an old man wanted to sit down. It'll probably be illegal too in a few months. On the bright side of NY'ers, they will usually give up their seat to the elderly.
erwin1978 - I don't think the Asians are most impolite. I find the ghetto types to be much more rude (yelling, cussing, etc.) The impolite Asians don't seem to realize what they're doing is impolite. But it's true, many asians (recently from asia) will fail to give up his seat. In fact, he'll make a mad dash from 5 yards away to get a seat while someone 2 feet away waits patiently for a person to get up.