Those dumbfucks at United Airlines.
It turns out the flight wasn't overbooked, it's just that four airline employees showed up at the gate after everyone had boarded, and said they needed to be on the flight.
The problem occurred when they decided to have airport security drag passengers off the plane to make room. They should have told the four employees they weren't going to be able to take the flight because they didn't give enough advance notice to the gate personnel - after passengers have boarded, it's a bit late for that shit. It was this arrogance, and the gate personnel catering to it that created the problem