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.
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.
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 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.
Maybe Naruto gets pissed off because his friends don't believe in him. For example, if they suspect him of being involved in something bad without evidence.
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 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.
First, the author should stay true to Naruto's character. By studying his traits like his determination, his loyalty to his friends, and his never - give - up attitude in the original anime. For example, don't make him a coward when he's known for being brave. Second, improve the plot. Make it more logical and in line with the Naruto world. No sudden, out - of - the - blue events that don't fit. Third, work on the writing quality. Use proper grammar and spelling so that readers can easily follow Naruto's journey in the fanfic.
One possible scenario could be that Naruto gets pissed off when he discovers someone has been spreading false rumors about his friends in the fanfiction. This would really push his buttons as he values his friends highly.
It could also be due to the fanfic's poor writing quality. If the grammar and spelling are atrocious and it's hard to follow the story. When it comes to Naruto, fans have high expectations. So, if they can't even understand what's going on with Naruto in the fanfic because of bad writing, it can lead to a 'pissed off' reaction.
Perhaps an outside force that manipulates the Young Justice team into going against Naruto. This could be a villain who wants to create chaos in Naruto's world. The Young Justice, being unaware of the manipulation, start acting in ways that piss Naruto off. In this case, the real antagonist is the behind - the - scenes villain, but the Young Justice members end up being the ones Naruto has to deal with directly, making them sort of antagonists in Naruto's perspective.