LPS Popular, despite being rated PG+13, has dealt with serious themes throughout the series in a realistic view.
Real life issues
This is the most common theme throughout the series. Through out Season 1 Brooke often bullies some students, with Savannah being her most common target. Brooke's common thing to do with Savannah is make fun of her weight by calling her 'wiener dog' or 'sausage'. Brooke at some point made up rumors about Savannah.
A secondary theme in the series. The know characters to have it are Brooke and Savannah. Savannah begin to starve herself in Season 1, though appears to stop at the beginning of Season 2. Brooke seem to have this disorder even before the series started.
Not much violence is shown throughout the series. However the theme had shown up in the Season 1 finale where Brooke scratched Savannah's face after she found her (Savannah) and Sage were making out, she scratched Savannah so bad that Savannah needed stitches. Violence made a return in Season 2 where Brooke and Savannah got into a fight which resulted in Savannah having stitches on her back and Brooke ending up at the hospital with a concussion.
This theme has not appeared in Season 1, but started its debut in Season 2. Its evident by Sage and Savannah's extreme make out sessions. As in episode 27 Genevieve's boyfriend, Nathan, had seem to only wanted her for her body. In the episode Make Up, Make Out, Savvy and Sage have an extreme make-out session, to a point where they are on a bed on top of each other. In the next episode, Nathan takes off Genevieve's scarf while they are kissing, which might imply that he is trying to possibly have sexual intercourse with her, and he is taking off her clothes.
Given the show was rated PG the language was limited in the show. However some characters use the 'friendly' versions of those words. Words such as 'Beauch' and 'female dog' had been use to resemble the B word, and 'Bark off' could be a reference to the F word.
Not much of this is shown, but in season 2 it shows that Brooke tends to mistreat her pet cricket, such as forgetting to feed her, take her outside so she can use the bathroom, even on one occasion leaving her cricket out all night while it was raining. Savannah then later accuses Brooke of being a 'cricket abuser'.
Like Animal Abuse this theme is less common. It's known that Brooke's mom, Ms. Hayes seems to be hardly home most of the time. Ms. Hayes seems to be less interested in what Brooke is doing. However this could be false considering the Ms. Hayes seemed to care for her daughter in Episode 24.
Savannah could possibly have the same issue considering that her father is never home. It could be true when in episode 24 Savannah said she hated her father right in his face.
Brooke has on occasion lied about Savannah. She also possibly lied to Sage, her mother, and even her friends.