I know we haven’t always been nice to you or whatever. And I really feel bad about it—I do.” I try to gauge what she’s thinking, but it’s like something has shut down behind her eyes, a button switching off, and she just stands there staring at me dully. I rush on, “The thing is, we never really meant anything by it, you know? I don’t think I—we—really thought about it. It’s just the kind of thing that happens. People used to make fun of me all the time.”
This is the line that opens the floodgates where you find out just how poorly Juliet was treated by the 4 friends. Their treatment of her actually meets the criteria for bullying, being sustained over time, involving a power imbalance and hostile intent. However, Lindsay seems confused herself, not knowing why it kept going on, saying she thought she would just have stood up for herself, while Juliet said she thought it would just blow over.
I get that passivity in the face of mob mentality leads to contempt, but it's supposedly high school, and to sustain that level of hatred over time suggests Lindsay had some serious mental health issues.

