Miscommunication is another big factor. Hermione might say something that Harry misinterprets, or vice versa. In a lot of fanfiction scenarios, Hermione's complex explanations might come across wrong to Harry, making him think she's being condescending or hiding something from him, which angers him.
One common reason is Hermione's over - protectiveness. Sometimes she tries to control situations too much, which can make Harry feel suffocated and thus angry. For example, in some fanfictions, she might try to stop Harry from taking risks in a dangerous mission, which he sees as her not believing in his abilities.
In the 'Harry Gets Angry' fanfiction, Harry might get angry when his reputation is smeared. He has always been in the spotlight, and false rumors can really get to him. Also, seeing the weak or the underdogs being bullied can make him angry. He has a strong sense of justice, so any form of oppression or unfair treatment towards others can stir his anger as well.
He might be confused at first. Harry isn't always the quickest to understand Hermione's motives right away. So he could just stand there, looking at her with a puzzled expression on his face, not really knowing what he did wrong.
It could be due to a misunderstanding. Perhaps someone spread false rumors about him, and as a result, people started treating him differently. He might be angry at everyone because he feels that no one bothered to find out the truth from him. Also, if there were some new rules or restrictions imposed on him without proper explanation, that could fuel his anger.
A major reason could be differences in their approaches to fighting the dark forces. Maybe in the fanfic, Hermione wants to use a more diplomatic and academic approach, Ron is hesitant and just wants to follow the status quo, and Harry wants a more direct and action - based approach. Their inability to reconcile these differences can lead to Harry being angry. For example, when they are planning how to deal with a new dark wizard threat, their arguments and lack of compromise can make Harry frustrated and angry with them.
One possible reason could be that Harry has been spending too much time on his heroic duties and not enough time with Ginny. Another might be that he made a decision without consulting her, like taking on a particularly dangerous mission. It could also be something as simple as he forgot an important date or anniversary.
Perhaps Hermione has her own plans regarding Runes. For example, she might have wanted to study Runes with Harry in a particular way or at a certain time. When Harry starts taking Runes on his own or in a different manner, it disrupts her plans, leading to her anger. Also, she could be worried that Harry's approach to Runes might get him into trouble or affect his overall academic progress in a negative way.
She could also lie to gain an advantage in a situation. Maybe there's a competition or a mystery they're trying to solve, and she thinks lying to Harry will give her the upper hand. For example, if they're competing to find a hidden magical object, she might lie about where she's looking to throw him off.
He might lash out with his magic. For example, he could send a spell flying at the source of his anger without really thinking. Sometimes, he just glares intensely, his green eyes filled with fury. And he may raise his voice, shouting at those who have angered him.
One reason could be differences in strategy. Harry may have a more direct or risky approach to fighting Voldemort, while the Order might prefer a more cautious, long - term plan. This clash in ideas can lead to his anger.
It could lead to a lot of conflict. His friends might try to reason with him, but if he's too angry, he might push them away. This could split their group apart, creating new alliances or just leaving Harry isolated for a while. His anger can also attract the attention of the wrong sort of people, like those who want to use his emotional state for their own gain.