Another reason could be if someone were to slander or disrespect his late mentor, like Iruka or Jiraiya. Naruto holds these people in high regard, and any negative remarks or actions towards them would likely enrage him.
One reason could be Boruto's recklessness. In fanfiction, Boruto might engage in dangerous stunts or actions that go against Naruto's teachings. For example, if Boruto were to use a forbidden jutsu without fully understanding the consequences, Naruto would be angry as it not only endangers Boruto but also those around him.
One possible reason could be that Tsunade makes a decision regarding the village that Naruto strongly disagrees with. For example, if she refuses to send help to a neighboring village in need, Naruto, with his strong sense of justice, might get angry. He's always been about protecting and helping others.
One possible reason could be misrepresentation of her character. In some fanfictions, authors might change her personality to fit a certain plot, like making her overly jealous or mean, which would be out of character for the gentle Hinata. This could make her seem unlikable and thus anger fans who love the original Hinata.
It could also be due to jealousy. If Naruto is spending a lot of time with other female characters, Hinata might get angry. Even though she is usually shy and reserved, her love for Naruto could turn into anger if she feels threatened by his closeness to others.
One possible reason could be that Konoha has made decisions without considering Naruto's opinions. Maybe they have made policies that Naruto believes are unjust towards certain groups, like the treatment of the Uchiha clan in the past. Naruto, who values fairness and friendship, would be angry at such insensitivity from his village.
In the fanfiction, it could be that Kakashi is being too hard on Naruto during training. He might be pushing him beyond his limits without proper explanation or support, causing Naruto to feel frustrated and angry. Naruto is a determined character, but everyone has their breaking point.
Perhaps Naruto has always felt different from others in the village. And when he finally learns about his parents, he realizes that their actions, even if they were for a good cause like protecting the village, still made his life very difficult. He might be angry that they didn't find a better way to handle things so that he didn't have to suffer so much growing up.
One possible reason could be a misunderstanding. Maybe Twilight accidentally disrupted some important plan of Celestia's. For example, if Twilight was experimenting with a new spell and it had an unexpected impact on Celestia's castle or a major event she was organizing.
Another reason could be related to school work. If there are new rules in Hogwarts that she deems unfair regarding academics, like restrictions on library access or new grading systems that don't reward hard work properly. Hermione is all about learning and fairness in education, so this could really make her angry.
His family might have neglected him in some ways. Naruto grew up alone and feeling unwanted in the original story. If in the fanfiction, his family was around but still didn't give him the love and attention he needed, it would be a valid reason for his anger. He has always craved connection and acceptance, and if his family failed to provide that, he would be furious.