One reason could be betrayal. If someone he trusted, like a fellow ninja or an old acquaintance, turned out to be working for his enemies, that would surely make him pissed. It's a huge blow to his trust, which is a big part of his character.
In the fanfic, Naruto might also get pissed if his ideals were being mocked or undermined. He has always strived for peace and acceptance in the ninja world. If someone were to say that his dreams were naive or impossible, it would definitely piss him off as he's put so much effort and heart into his beliefs.
Another factor could be the threat to his loved ones. Naruto is extremely protective of his friends and family. So, if an enemy were to target them directly, it would send him into a rage. He'd be pissed off at the audacity of the enemy to go after those he holds dear.
The fanfiction might change the important events in his life in a way that he doesn't like. For example, if it rewrites how he became a ninja or his relationship with his teacher, Iruka. These are fundamental parts of his story, and if they're distorted in the fanfiction, it's understandable that he'd get angry.
A new, powerful and arrogant villain introduced in the fanfic could be the cause. This villain could constantly mock Naruto and his ideals, and try to undermine his efforts to protect the village. Such blatant disrespect would make Naruto really pissed off as he is very protective of his home and the values he stands for.
Well, in a 'naruto gets pissed fanfic', Naruto might get angry over various things. It could be because of an enemy taunting him about his past, like how he was an outcast in the village as a child. He could also get pissed if his friends were in danger and he felt powerless to help them right away.
Sasuke could be a possible cause. If Sasuke were to go back on his word about protecting the village or if he were to harm their friends again, Naruto would be pissed. Their relationship is complex, and Sasuke's actions often have a strong impact on Naruto.
Sasuke could make Naruto pissed off if he goes back to his old ways of seeking power and revenge. Naruto has worked hard to bring Sasuke back to the right path, and if Sasuke strays again, it would surely anger Naruto.
Sasuke could be the cause. If Sasuke were to betray Naruto again in the fanfiction, it would surely make Naruto pissed off. Their relationship is complex and Sasuke's actions have a big impact on Naruto.
The 'Naruto pissed fanfic' are popular because they can show Naruto in situations that are more extreme. When he's pissed, he might act in ways that are unexpected, like challenging the authority or making bold moves. This creates a sense of excitement and unpredictability for the readers, who are always eager to see their beloved character in new and challenging situations.
In a 'naruto gets pissed off fanfic', one possible scenario could be that Naruto discovers someone has been slandering his friends behind their backs. He would get pissed off and confront the person directly, his eyes blazing with anger.
One scenario could be when Naruto finds out that someone has been spreading false rumors about his friends. This would surely make him pissed as he values his friends deeply.
Maybe he'll go on a rampage in the fanfiction world. He could start using his powerful jutsu to show his anger, like unleashing a Rasengan on the source of his annoyance.