Is this a reference to something specific or just made by someone who doesn't ride the subway? Feels vaguely "the cities are from infested hell holes!" conservative pearl clutch to me, but maybe I'm out of the loop.
Or just a joke. I live in a city with a metro system, I use it, and as much as I've never personally seen a fight in the metro itself, they obviously happen. Some users are stabbed a few times a year. I've seen people jump over the tracks. I've felt a bit threaten by a beggar that I've once said I recognized.
And I'm not living in a very criminal city. I'm not saying the metro isn't safe, or that you'll see fights and brawls for the price of a ride, but it could happen. Like, take the metro when bars are closing and there's probably gonna be higher chances to see a brawl or a fight. I imagine it's similar in bigger cities with metro/subway systems as well.
And I want to stress that cities where this can happen are not inherently dangerous. There are much smaller cities that have a highest crime rate than the closest metropolis, but they don't have the density for a metro/subway system where you can thus see drunk people fight about something they already forgot.
I assume they choose NYC in particular because its a three letter acronym that could sound like it would fit in with other three letter fighting organizations.