This is a subjective question and many part of the world will answer it differently. I want to pick example of one of my work bosses. Why I think that he is a douchebag:
Dismissive and ignorant
He is one of the most ignorant persons I have ever worked it. He was not only dismissive to me, I have seen being dismissive to many people below or parallel in position. For example, I repeated saw him denouncing managers parallel to him. One example of his dismissive behavior is when he was badmouthing about PhD in front of me like this — “ Ph.D. is just a overkill. Don’t ever do it.” It might be true for some job, but he was advising someone not to do Ph.D. where two of his direct reports (he had three direct reports at that time) are Ph.D. and are paid in top 10 percentile in the 5000 employee company. I felt that he has a inferiority complex of having no pedigree (pedigree is horseshit IMO), but he would try to cover it with asshole behavior.
Not recognizing people
This guy never said “good work” to me even when I made him deals of $MM or solved a hard technical problem. I heard same things from my colleagues who worked with him. He had a natural tendency of taking/ stealing credit for anything that gets done.
Showing off hierarchical power
This is another tool of the assholes. The guy used his “higher” position to get things which he should have and always managed “up” and berated “down”. He was super nice to his bosses and super uncool to people who is “down” from his position.
No empathy
I have seen the guy to be empathetic sometimes, but in general, he would put extreme targets and would scold his employee if s/he can’t earn the badge. He would care less about someone’s personal stuffs and always take advantage of any favor he would have ever done.
Unethical
The guy was reported to HR by one of our colleagues for unethical asks regarding a customer. He asked me to download reports for Carpenter from UofM which is paid by the University. The worst part was that he wasn’t interested in asking me if I am ok to do it, but he had a conviction that I should have no problem doing that. He always crossed lines and never respected employees who doesn’t want to cross lines.