The simple answer is that it makes us feel good about ourselves.
We love knowing the city and the subway well enough to tell you how to get wherever you're going. It's even more of a rush when you ask two of us and then we get to debate in front of you whether taking the 4/5 to the 2/3 at Bergen St. or taking the Q to 7th Ave. is the best way to get to Flatbush Farm, or if it's better to talk one block to the F train or to take the tram to Roosevelt Island. Not that tourists go to Roosevelt Island, but you get the gist.
We love that we know how to get around this sprawling, crazy city, and by god we're going to demonstrate that to you.
The New York Times recently ran an excellent article on our dear subway and how tourists think it's like descending down the Styx. Yeah, it's hot down there. Sure, it's filthy. Granted, sometimes you wait forever for the Q train or find yourself sandwiched among so many travelers that someone is actually touching your body on every single side... But having been a Manhattan car owner, I'll take the foibles and stench of public transportation over that 45-minute parking odyssey any day.
In spite of the run-down stations and the Carter-era cars, there are improvements being made on the subway: I RODE ON A BRAND SPANKING NEW N TRAIN!
It was so new there weren't even scuffs on the floor. Not a speck of dirt. And get this - they had a digital display next to the digital list of stops we were approaching in order (no more guessing which direction you're going!), and that digital display showed videos of how neat-o the new trains were! And to top it all off it was like twice as wide as the former nicest trains on the subway - the ones that run on the 4/5/6 and the 2/3 (occasionally). I hear the L trains are nice too, but I can't really imagine an occasion when I'd need to ride one. I'm a sorry excuse for a hipster.
It renewed my faith in the subway. Now if they can just wash down those platforms or something. Anything. And maybe install some fans.