Let me expound on my post by presenting counterpoints to this.
In stable cities, neighborhoods develop organically (though this is helped by sensible design and hampered by overly systematic, commie/grid style layouts), so the city starts to behave as series of small towns, which just happen to be so physically close they are adjacent, with most townies working out of town at a major commercial center which in turn is also superimposed geographically.
This is still possible with strangers if there is some conformity, and people adhere to some standards.
Standards of etiquette, manner of dress, even accent and language all help produce this cohesion, even if seemingly superficial and orthogonal.
However NYC is infamous for its lack of conformity. It is, as is well known, a melting pot of all sorts of people. Take a 20 minute subway ride and you will meet all kinds of weirdos. There is an endless array of speech (from upper class white accents to incomprehensible bix nood), dress (half naked people, hobos dressed in rags, hipsters, nogs with pants hanging around their knees, goths, suited businessmen, teenagers with motley getups), behavior (people acting stiff but polite, drunks, high junkies, thugs, loud college bros, shrill teenage girl gangs, stuffy old jews, hipsters and performers just randomly dancing and doing cartwheels in the streets, tourists of every variety) not to mention race and so on.
In a more homogeneous city, you can meet a stranger and say "okay, I don't know this person, but he looks like my neighbors, talks like my neighbors, acts like my neighbors, I think I can find common ground with him same as I do with my neighbors" and it works. But in NYC there are as many kinds of people as there are people, you can't ever know what to expect.
Of course an absolute monoculture is not necessary, some subcultures are fine. Imagine a Swiss mountain village of 200 people, perfectly homogenous, everyone looks the same, behaves the same, all families have lived there for generations. Let's say this village is isolated one day by an avalanche. Will there be disorder and chaos? Of course not, looking at the people you wouldn't know anything happened at all. Life will go on exactly as before.
Now imagine if a group of 30 Japanese tourists happened to be in the town when this happened. Obviously they are strangers and are nothing like the locals - but will chaos ensue? Again, no. While the tourists are utterly foreign to the villagers, they within themselves have a common culture. The villagers can learn this, and then use this as a mental category to deal with all the tourists smoothly. So again order will continue, despite the rift in culture and lack of familiarity.
But in NYC you cannot do this. There is an endless array of different "types" of people, it's like a zoo. Every time you meet someone, you have to make a new category in your head for them, and you hardly ever meet someone who can be filed under the existing categories. So now you are inflating your list of mental categories beyond your mind's capacity, and you can only afford to learn the most basic of social skills for interacting with each category. Which is why New Yorkers are so socially primitive.
When order reigns, the legally imposed standards of behavior act as a kind of supercategory that provides surrogate common ground to people. This is why the city can function, but the residents are alienated and do not feel intimacy or belonging. But when crisis removes the authority, this supercategory vanishes with it, all that remains is the extremely basic modes of interaction reminiscent of prehistoric cave people.
