Lonely in a sea of humanity? Urban dwellers encounter so many forgettable people on a daily basis that they feel entirely anonymous. It is funny to be surrounded by people, but to not notice. Faceless faces.
Within that sense, we tend to not care much about about our behavior in public. People who would never be rude to their friends or acquaintances, have no problems behaving horribly towards strangers. They feel they won't ever see them again, so why bother being polite.
The bigger the city, the better the odds of not seeing those people again. As more people congregate in larger groups, their behavior when they are alone degenerates.
It can be wonderfully horrible in a big city to observe just how low people will let their behavior slide. It is not just that sense that the other people don't matter, so you shouldn't bother to be nice to them; some people actively go out of their way just to behave poorly to others.
On crowded city streets it is noticeable, but it reaches its zenith in big repeating crowds for things like buses, or subways. Constant aggravation makes people cranky. Stir and repeat, and then they get ornery.
Sadly, their distemper, frustration and rudeness only make bad situations worse. It can spread through a crowd like a bad cough; feeding on itself as it grows. Tired cranky zombies marching back and forth between their occupations and their lives.
If you really want to see humanity at its absolute lowest point however, you need look no further than the roads and highways. If people feel anonymous in a big city, they feel invisible and anonymous in their big cars. Nothing is stupider than an impatient driver whipping around nearly a tonne of metal, plastic and glass in an uncontrolled frenzy simply because they are five minutes late for dinner. Why more people don't die in automotive accidents is a great mystery. Even just a bit of congestion and the crowds go wild. If it wasn't for the fatal consequences, streets would become totally unnavigable during rush hour. It is always such a low for humanity.
Most of us make our own problems in life. And so many of us together make our own misery. It is this strange obsession in modern life about trying to get ahead, and maximize our potential that fuels our angst. When you are too focused on the little aggravations in your life, you miss those big grand wonderful things floating around you. Trying to be a little less rude, each and every day is a great way to combat the funk that people are in, and to increase ones own karma. We all feel some need to contribute in a positive way to humanity, which we can actually do with the smallest of efforts. Making the world a better place starts with not pushing people out of the way while bordering a bus. It is not a difficult concept.