I've read volume after volume after volume after repetitive volume of shoujo, and I can assure you that the answer is:
There are tons of them. One of these things is bound to happen:
* The hottest guy in the protagonist's high school is in love with her.
* Said guy has no personality apart from his interest in the girl.
* Or he has a dark and tormented past.
* The two take forever to get together. "I love you! You love me! Let's not say it 'till book 3!"
* A rival for the protagonist's love appears.
* Some other girl is also in love with the hottest guy in school, and is determined to steal him away...
* ...so she kisses him against his will in front of the protagonist, who thinks the guy is doing it voluntarily. She runs away before he gets a chance to explain.
* A teacher says the girl and the guy aren't allowed to be together, since it's against school rules.
* The guy is hanging out with his sister, and the protagonist assumes it's a date and he's cheating on her.
* When the protagonist is out on the street, a couple of guys she's never met before try to pick her up. When she tries to politely decline their advances, they won't take no for an answer. Things get rapey, but before it gets worse than PG-13 the hottest guy in school beats them up and chases them away.
EDIT: Oh, and there's usually some university entrance exam that the protagonist wants to pass.