My god, people are just awful, aren't they? And when we say "people" we, unfortunately have to include ourselves in that.
As it turns out, people aren't just awful in day-to-day life, as well as all of the anecdotal evidence that we have, they're also jerks when you study them in the lab. There have been numerous scientific studies into the darker side of human behaviour, and a lot of them have forced us to come to the conclusion that we're a mean, selfish, stubborn bunch of cynics who would trust their own grandmothers as far as they could throw her.
A lot of this dark side to human nature can be traced back through our evolutionary roots and, at one point, probably served a useful purpose. In our modern world of bus stops, rush hour and Donald Trump, however, they get channelled into being generally awful to one another.
Like, we've done some good stuff too, curing smallpox was pretty good, Mother Teresa was a canny lass and all, but light without the darkness is blinding and luckily we're all doing our best to balance out the good in the world by being terrible people. And you'll be pleased to know that it all starts at birth...