While New Yorkers don't mind correcting you, they also want to help you. In the subway or on the sidewalk, when someone asks a passerby for directions, other people, overhearing, may hover nearby, disappointed that they were not the ones asked, and waiting to see if maybe they can get a word in. New Yorkers like to be experts. Actually, all people like to be experts, but most of them satisfy this need with friends and children and employees. New Yorkers, once again, tend to behave with strangers the way they do with people they know.
From Joan Acocella in Smithsonian Magazine, on why New Yorkers seem rude, but are really just acting familiar with strangers.