These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Jerkass Woobie: David. He bullies Jane and overreacts to things like her getting an internship, behaving as though it's a major betrayal. He also takes advantage of a drunken Sloan at the party, which not only devastates Jane but also upsets Kate. However, he does seem to care about Jane and he has a Freudian Excuse.
Moral Event Horizon: It's hard to say when Langley crosses this; she tries to kill Jane for for pretty petty reasons, she manipulates Jane, Kate, Ollie and several other characters for a long time, she pushes her own grandfather down the stairs, hospitalising him, because he wouldn't buy her a new car. And she bugs Jane's room, and comments on how amusing it was to watch her freak out and convince everyone she's crazy.
Arguably, Jane's previous boyfriend Liam crossed it when he started dating Jane just to keep her quiet about her suspicion that Bonnie's death was not suicide.
Although Langley dismisses it, it's implied that her grandfather raped her mother, his ''daughter''. Langely says he mother was a whore, but considering her mother chose to flee to Arizona with her infant daughter and live in poverty rather than face her parents, it seems unlikely Langley's mother was a willing participant.
Paranoia Fuel: A lot of things that happen in the book, especially since Jane keeps seeing and hearing threats, but is plagued with self-doubt and told she's imagining it or reacting badly to her medication. Plus the concept of being watched that appears frequently throughout the novel.