People hate Jenny the most because they probably have seen a Jenny in their lives. Joker, Hannibal and Vader are too removed from normal life to genuinely hate.

I just hate Skylar because she sang happy birthday uncomfortably and it legit made me not like the character ever again lol

Yeah, I can't understand anyone who doesn't come away with a deep sorrow for her character - certainly compared to infinitely lucky forest. She tries so hard to be a good person despite everything awfull happening to her every single time, he just does what he feels like and every time he has the best luck ever.

I wouldn't put what Skylar did anywhere on Jenny's level.

That said, Jenny's trauma was a lot worse and affected her over her entire life.