There's never any reason to smile when you're waiting for the subway fairly late at night, like between 10 pm and 12 am. No reason at all, unless you are standing there in the heat with a friend, able to talk and pass the time over the course of the 10 minutes to half hour that you are waiting.
I used to defend the subway, even at night. It used to be so reliable, and so much cheaper. But this summer they raised the price of a metro card and slowed down or eliminated most services. And maybe the heat slows the trains down too? Maybe by the time you got to the platform, you just missed it and the next one is delayed because of... the poor economy? (This always happens to me.)
Either way, sometimes you have to get creative and entertain yourself when waiting for your ride home to take you home. There are plenty of people around who are waiting too, but they are strangers, so all you have is your iPod, the games on your phone, and sometimes your camera. Despite the trash and rats and weird leaky things hanging from the ceiling, there are photo opportunities even in this underground dungeon.
Some are smiling right at you, so go ahead and take their picture!
(light bulbs hanging from the ceiling at the 42nd Street NRW station)