One possible reason could be a misunderstanding. Maybe Percy did something that Annabeth misinterpreted, like making a decision during a quest without consulting her first, which made her feel disrespected.
Maybe she's jealous of Percy's popularity at school. It could be that he always gets more attention, whether it's from teachers or other students.
One possible reason could be jealousy. Maybe Percy gets more attention or recognition in their fictional world that makes Annabeth envious and thus appear to hate him.
One possible reason could be that the fanfiction misrepresents their characters. Maybe it portrays Percy in a way that Annabeth doesn't like or goes against the essence of their relationship as she sees it.
One possible reason could be jealousy. Maybe Rachel has something that Annabeth wants, like a closer relationship with a particular character. For example, if they both like the same guy, Annabeth might hate Rachel out of envy.
One possible reason could be competition. Annabeth is highly competitive and Percy's sudden appearance and his own skills might make her feel threatened, leading to hatred. For example, if he outperforms her in a training session or a quest task.
One possible reason could be jealousy. Maybe she sees Percy getting more attention or praise than her in the fanfic world, and that envy turns into betrayal. Another reason might be a misunderstanding. For example, if there's some misinformation spread about Percy that makes Annabeth believe he's done something really bad.
Another possibility is that Percy made a really stupid mistake that endangered himself or others, and Annabeth, being the more level - headed one in some ways, slapped him to snap him out of his foolishness. For instance, if he rushed into a dangerous situation without a proper plan, Annabeth's slap could be a wake - up call.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
It could be that she secretly likes the smell of it, which is a bit of a personal and intimate reason. In the context of the fanfic, it might also be a symbol of their relationship, and by stealing it, she's making a statement about how she feels towards him, whether she realizes it fully or not.