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.
Derailing Love Interests: due to the constantly changing love interests in Erica's life, her current love interest often gets derailed after a period of perfect happiness in order to justify her developing feelings for someone else. This is particularly evident with Ethan; first several issues about their sex life crop up, then he gets extremely jealous about Kai and demands she stop being friends with him, then he refuses to support Erica in starting her own business, causing their break up.
Ear Worm - Alien as performed by the in-show musician, Kai.
The theme song.
Everyone Is Jesus in Purgatory: One of the more popular Epileptic Trees theories for the show is that the latte that hospitalized Erica in the first episode killed her, the therapy was her purgatory, and that she will go on to become a therapist like Dr. Tom after Season 2's "cliffhanger" ending. The Season 3 premiere reveals that Erica is indeed being trained to become a therapist, although the other part of the theory has yet to be confirmed.
It's probably worth noting that Dr Tom became a therapist after a suicide attempt that might have killed him.
Adam also entered therapy after literally dying and being revived by paramedics.
As did Kai, who overdosed.
Fan-Preferred Couple: At least on Tumblr, Kai/Erica was this. This may be due to the fact that, after Kai's initial frostiness, he didn't need to be negatively derailed like other love interests because there was already an obstacle to keep Kai/Erica from happening: they live in different times. Because of their status as fan preferred couple, few fans were happy with the treatment Kai received in the fourth season. Though he made a return, apparently due to fan demand, Erica only seems to hook up with him out of spite after Adam breaks up with her, and after a short time she breaks up with Kai, citing the time problem, to get back with Adam.
The Scrappy: Part of the fanbase consider Adam to be a mixture of this and a Creator's Pet, due to the strong focus he receives in the final season, often coming at the expense of Erica's plotlines. His relationship with Erica is similarly disliked by many due to their incompatibility, as most of the relationship involves Adam arguing with her and ignoring her problems for his own.