Why are so many college aged “adults” so whiny and entitled, complaining about their bosses?

They're the same ones who complained about their teachers while not doing the work they were assigned, or even trying. There are also some young people who complain about their teachers and have quite legitimate complaints, and this extends into adulthood. So judge people as individuals. But there is a problem with a lot of people thinking they can get a reward for no effort. Where they learned it, I don't know.