1. He asked you out somewhere cool. You met him while pondering the same Chuck Close piece at the Met, or while he was working as a dog walker in Washington Square. He caught your eye as you stood waiting on the myriad-like line of the Union Square Trader Joe's, or did body shots with you at a Bushwick warehouse rave. There is also the high likelihood the he is a coworker (and you find time to rendezvous in the supply closet), or that he bought you a drink at any one of NYC's gajillion bars.
2. He asked you to move in with him before he said, "I love you." New Yorkers are always looking for roommates to cut down on their living expenses. When his college buddy decided to teach English in Myanmar for a year and needed to sublease his 5x7 bedroom, it made sense to ask if you'd like it first. More common still is to be asked to move in when there isn't an empty room, just an empty side of the bed, because three people splitting $3,000 a month for a two-bedroom apartment in the Lower East Side is a cheap solution to an expensive problem.
3. The sex is pretty diverse. Sex with a New York boyfriend is always exciting because city dwellers come from all different states, countries, and cultures. Dating the reserved fashion model from South Africa provided you with a very different sex life than when you coupled up with a hippie dude from San Francisco, who used to live on a commune. You didn't even know you could do that thing with your thumb until you dated the 20-something intern at your law firm.
4. He's loud. "DO YOU WANT MILK IN YOUR CAWFEE?" Simple questions cause you to wince from the volume of his voice on a daily basis, but after a while, you understand that your New York man isn't trying to verbally assault you -- he's just used to screaming over the music at sports bars, yelling salutations to friends across subway platforms, or being shouted-at by his overbearing boss. He also talks with his hands, might say "fuck," "bullshit," and "jabroni" a lot for no reason, and if he's really a hardcore New Yorker, he's got a regional borough accent that is both endearing, and annoying.
5. He's always the best dressed. Tailored trousers, fitted blazers, facial hair shaved in the latest style that would otherwise look disheveled elsewhere - New Yorker boyfriends always overdress for a funeral, or look fashionably underdressed for a show at Lincoln Center, but they always look good. You'll spend hours trying to make sure that you aren't mixing a 1980s dress with 1940s shoes, because he will point it out.
6. He doesn't have a valid driver's license. He might have an ID, sure, but ask him to drive you anywhere, and his mind might explode. "Can't we just take the train? The train goes everywhere." Except to that cabin in the Catskills which looked super romantic, but is nowhere near a train station, bus depot, or taxi stand. He probably failed his driving test a few times because he freaked out during the parallel parking component.
7. He is down to try anything. New Yorkers are overstimulated by their surroundings, so there usually isn't an experience not worth having. He'll rock a trapeze lesson at Pier 40, taste chicken feet in Chinatown, accompany you to a Hedda Lettuce drag show, and even sit through the Sex and the City on-location bus tour, if that's what his baby wants.
8. Or, nothing is good enough for him. "This hot fudge sauce isn't as fudgey as the kind at Peter Luger's," he'll sneer at the dish of ice cream you decided to share at City Diner on the Upper West Side. New Yorkers have access to pretty much everything, from 1920s Jazz Age lawn parties on Governor's Island, to companies that will deliver dildos to your doorstep in an hour. It's not surprising that a New York boyfriend's standards can be so damn high, but it can be difficult to come up with creative date ideas all of the time.
9. He likes to flash his cash. Men in New York will fight you when it comes to paying the bill for Sunday brunch. They are always the first to buy a round of drinks, they have piles of gadgets, gourmet mustards, and IOU coupons from local Kickstarters, and they've perfected the art of dropping change into a homeless person's cup without breaking their stride. New Yorkers complain about how much money they don't make, but they still make more money than if they lived elsewhere in the USA, and they feel good about being able to spend it freely.
10. His marriage proposal is super cliché. If he popped the question at Central Park, the Empire State Building, the Rockefellar Centre ice rink, Yankee Stadium, or Magnolia Bakery, congratulations, you're dating a New Yorker! New Yorkers would not be caught dead in these quintessential city icons otherwise, but there is something romantic about using the Brooklyn Bridge as the backdrop to what will hopefully be the 21st century version of When Harry Met Sally. If he could set up a breakfast at Tiffany's and propose there, he would.