I have only ever genuinely hated three people in my life.
One is an older relative. For decades I thought he was fine, he just didn't want much of a a relationship with me. Then a can of worms was opened and I learned how abusive, narcissistic, and selfish he is--and kind of sexist to boot. He is a chameleon who blends in exceedingly well with whatever social group he chooses--including his own family. He hurt people I love so deeply that I still seethe when I look at him, even if they've forgiven him. I smile at him over Zoom and he smiles back, but those smiles are only skin-deep.
One was a co-worker. We worked together in a residential setting over the summer, and I got to watch her treat her wilted, desperate boyfriend like shit, flirt incessantly with other men, flaunt the organization's rules for interacting with children, and expose said children to a whooping cough. She later claimed we misunderstood her and that her doctor only said he THOUGHT she had whooping cough... but she only said this after we'd done an awful lot of work to start informing parents and making sure the kids would not get further exposure. Just an all-round inconsiderate person.
The last was my boss. My hate for him was completely unjustified in retrospect; I was going through a lot and I shouldn't have projected it onto him. It felt like he was stymying my work at every turn... and he was, but it really came down to a difference in working styles, and I was having trouble adjusting to the slower, more deliberate pace of the office. I think if I worked for him today, we'd get along just fine. At the time, though, I just wanted to scream and throw plates when he made me miss yet another deadline.