Every school's different. But I remember from my high school experience, several things I hated:
The "alternative just for the sake of being alternative" crowd. Every school has these gother-than-thou types. (And their look is always goth.) Look for scarred forearms, because they're the only people who cut themselves AND tell everyone.
Pop quizzes. I've heard it from every teacher who logically can give a pop quiz: "If you did the homework, you should be fine." Why do teachers lie?
Relationships that didn't work out. But it was high school, so there was more cheating than a daytime soap opera. But between my friends and me, we still learned there are many many more reasons to end a relationship.
The schedule. Sometimes I had to get from one end of the school to the other in 3 minutes. Stupid computer randomized our schedule like that.
Detention. Surprisingly, not at all like The Breakfast Club. I'm not Judd Nelson, and I never hooked up with Molly Ringwald. No, instead we just sat there while the principal watched us. Yay.