Perhaps it's part of their banter. In their relationship, they often tease each other. Annabeth calling Percy stupid could be a form of affectionate ribbing, not actually meaning that she thinks he's truly stupid but just a way to playfully get on his nerves.
Perhaps Percy refuses to take on a certain task that Annabeth believes is crucial. It could be something related to saving a friend or retrieving an important item. His refusal might seem cowardly to Annabeth, without her realizing that Percy has some other valid concerns or reasons for not doing it right away.
He might get defensive. Percy has his pride, and being called stupid would likely make him try to defend his actions and decisions.
It could be that she's homesick. Despite all the adventures, sometimes the longing for home can be overwhelming. Percy would comfort her by sharing his own feelings of missing his mother and how they can make new homes with their friends. He might hold her hand and tell her that their friends are like family now.
One possible reason could be miscommunication. Maybe Annabeth made a decision without consulting Percy in the fanfiction, and Percy felt left out or betrayed, leading to his screams.
There could be. Fanfiction is a vast world filled with countless interpretations of characters' relationships. Writers might create scenarios where Percy calls Annabeth sweet during a tender moment, like after she's achieved something great or when they're having a private conversation. It's all about exploring the characters' emotions and interactions in ways that the original books might not have fully delved into.
Some characters might be happy for them. For example, Grover could be glad to see their relationship growing. He might give them a knowing smile or a little nudge to show his approval.
It could be that he's lost someone important. Percy has had many friends and family in his life, and if he loses one of them, it would be a huge blow.
It could be jealousy. Maybe Annabeth is getting more attention in school, like from teachers or other students, and Percy, feeling left out or overshadowed, resorts to bullying as a way to bring her down.
One possible scenario could be during a battle. Annabeth might call Percy Perseus to inspire him, reminding him of the great deeds of the original Perseus. It gives Percy a sense of connection to his mythological past and boosts his confidence. Another scenario could be in a more private, emotional moment. It might be a way for Annabeth to show her deep understanding of Percy's identity as a demigod, using this more formal and myth - related name to convey her feelings.
One possible reason could be Percy's natural leadership skills. He often takes charge in dangerous situations and gets a lot of attention for it. Annabeth might be jealous because she also wants that level of recognition.