(New York Stories 2)
One of the best parts of working in Times Square was that you could get anywhere in Manhattan in less than 20 minutes. Despite this, after-work dinner always ended up being either around Union Square, East Village, Chinatown, Chelsea/West Village, or Williamsburg, where I would take the Q express to 14th Street, N/R local to Astor Place, Q express to Canal Street, 1 to Christopher Street, or the Q to the L to Bedford Station, respectively. Anyone who lives in New York comes to know its subway system like the back of their hand, because the subway could either be a huge waste of your time or an incredibly efficient mode of transport, depending on how well you knew it.
And so New Yorkers have always prided themselves on how well they knew the streets - because this was the clearest measure of telling true New Yorkers apart from well, those who aren't. The first thing you learn is that "avenues" always ran parallel to Manhattan, while "streets" run horizontally, forming perfectly rectangular streets (for the most part) with numbering that increased from East to West, and from Downtown to Uptown. As a result, you will never see a New Yorker look at a map, because a New Yorker always knew where to go provided they were on an intersection with two streets in view (so an avenue and two streets - and if you didn't, you walk until you get to an intersection). Likewise, a New Yorker never gives a cab driver the exact number of a street, but rather an intersection of a street and an avenue, always abbreviating them to simply their numbers "14th and 5th", with the street always coming first.
The above is unequivocally the #1 unspoken rule about New York. The rest you can read in New York Basic Tips & Etiquette, which are hilarious because they are actually true.
The second could be a lot of things, but it usually involves information and how to do things more efficiently.
So that would include how to tell apart those who will take 2+ attempts to swipe their metro card from those who can successfully get by on the first try (strip needs to be facing towards you with good, constant contact throughout the swipe); exactly which exit to get off at to bring you to which street, including the 8 different ones at West 4th Street that still utterly confuses me (because you can end up at Washington Square Park or West Village, depending on which one you get out at - then good luck finding your way through the diagonal/criss-cross streets that are...no longer numbered); understanding which metros do not work on weekends, and which do (because being late to a restaurant because of train problems is such an overused excuse); knowing which restaurants don't take reservations, and the exact wait time for those on a Saturday versus a Wednesday night; a visual in your mind of the exact locations of at least five Starbucks' within a five block radius around your work and home; and of course, how to hail a cab - because the number of times you see a tourist furiously waving at an unlit cab, angry that it doesn't stop for them ("if light is off, there is someone in it" is unfortunately not universally understood) has become all too common.
And finally, New Yorkers, complain. A lot. But if you ask any one of them after they left whether they missed the city, the answer would still be an unwavering, unequivocal "yes".