I have seen a pair of TSA agents at an airport screaming at a disabled woman in a wheelchair, because she didn't move fast enough for them. I've also seen CBP agents randomly harassing people at the Canadian border crossing.

And I've seen a guard in the American consulate in Vancouver berate people who were queued up for their visa interviews, early in the morning. The guy opened the door, said "Good morning!", and then stood there and waited. When nobody responded, he proceeded to tell the crowd that they should "get used to how we do this in America" before they get inside, and basically wouldn't let anyone in until the crowd chorused "Good morning" back in response.

My overall conclusion is that either the hiring practices for all these agencies are intentionally skewed towards that kind of employees, or that the lack of any meaningful responsibility quickly turns people into power-tripping assholes. Perhaps it's both.