You can never hail a cab on Friday afternoons - between 4 and 8 it's useless to try (only tourists try) Thankfully the subway doesn't close.
Avoiding Time Square in an unspoken rule.
You only go near Penn to leave town.
If you don't know where the 33rd street Path station is you'll never find it alone at night - it's in a little park of sorts, no huge signs or subway markings - yet it's always packed at night.
Open the fridge/freezer of a NYer - they have a bottle of water and a bag of edemame - but they have beer and wine.
At least 2 of everything - baseball, football, basketball - a region of choices.
Referring to neighborhoods like they're cities of their own "Yea we are heading to the Village then might get up to Hell's kitchen later" or "I'm in the Lower east right now, but I can meet up in SoHo?"
Living "in the 80's" etc. is a location not a time. Tons of young people in the UES (upper east side).
Lots of abbreviating like you would in texts or how people identify a city with an area code in the south or west coast - Upper east side becomes UES, Lower LES, Jersey City is JC, Long Island is the LI
Smells: you jump from the sewer, to the smell of a nuts for nuts cart, the awful fish smell in the bottom of China town, to the smell of pretzels to the smell of the subway versus the path train.
Summer: Turns NY on broil - fire drills in July in the heat, laying out wherever there is grass, pretending that your rooftop is the beach