Maybe he had a bad day at work or got into an argument with someone.
It could be that someone spoiled her favorite show or she didn't get the toy she wanted. There are countless reasons that could make a cartoon girl pissed off.
You can start by sketching the basic shape of the cat. Focus on its facial expression, like narrowed eyes and a snarling mouth to show it's pissed off. Then add details like fur texture and maybe some angry lines around its body.
Cartoon pissed eyes usually have narrowed pupils and raised eyebrows to show anger or annoyance.
For pissed off vegetable cartoons, you'd often see them with crossed arms, gritted teeth, and maybe even steam coming out of their heads. The way they're drawn could be a bit exaggerated to really show that anger. Also, the background might be gloomy or chaotic to match the mood.
The features might include exaggerated expressions, maybe frowns or angry eyes, and a kind of twisted shape to show their pissed-off state.
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.
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 she had a bad day or someone was mean to her.
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.