Well, maybe Gohan gets angry because Hercule takes all the credit for saving the world when in fact Gohan did a lot of the real work. In fanfiction, the writer might play up this injustice, making Gohan seethe with anger at Hercule's false bravado.
It could also be that Hercule constantly undermines Gohan's efforts in training or his role as a protector. He might make fun of Gohan's more studious approach to power, preferring his own showy but less effective ways. This kind of disrespect towards Gohan's way of life and his contributions could be a major source of anger for Gohan in fanfiction.
It could be due to unfair treatment from teachers. For example, if he's blamed for something he didn't do just because he's a Saiyan or has special powers. Teachers might be prejudiced against him, which would lead to his anger. He's a good - hearted person but constantly being misjudged would surely get on his nerves.
One possible reason could be that Videl does something that endangers herself. Gohan, being protective, might get angry out of fear for her safety. For example, if she recklessly jumps into a fight without proper training or preparation.
Perhaps Hercule tries to train under Gohan in a really clumsy and disrespectful way. He doesn't follow Gohan's instructions and constantly brags about his own non - existent skills. This could lead to Gohan snapping at him out of frustration for his lack of discipline and respect.
Maybe Chi - chi is constantly comparing Gohan to Goku in the fanfiction. Gohan has his own identity and abilities, and being compared all the time can be frustrating. He could get mad because he wants to be recognized for who he is, not just as Goku's son. Also, if Chi - chi is interfering too much in his training or friendships, that could also lead to his anger.
Cell - like characters are often antagonists. Since Cell was such a major foe in the original series, new versions of Cell - like beings could be created in fanfiction to make Gohan angry. They might target his loved ones or the Earth itself, provoking Gohan's rage.
Another scenario might be when someone undermines his power or mocks his Saiyan heritage. Gohan, having grown up with a sense of pride in his Saiyan roots, would get angry and show his true strength to prove them wrong. He might also get angry if he sees innocent people being bullied or oppressed, as he has a strong sense of justice.
One possible reason could be that the Cullens make a decision about her future without consulting her. For example, if they decide she should leave Forks for her own safety without asking her how she feels about it.
However, it could also be a turning point. If Gohan realizes that his anger is misdirected or if he communicates his reasons for being angry to Videl, it could strengthen their relationship. They could learn more about each other's boundaries and grow closer as a result.
One possible reason could be that Erza might have taken on a dangerous mission alone without informing Natsu. Natsu is protective of his friends and would get angry if he thought Erza was putting herself in unnecessary danger.
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.