The main reason could be the exploration of his own character in different fighting situations. In fanfiction, Gohan can be portrayed in various ways during fights. It could show his growth, his struggles, and his victories in ways that the original story might not have fully explored. Additionally, he might enjoy seeing how other writers view his fighting style and how they develop it further in their fictional works.
One reason might be that the fanfiction doesn't capture the essence of Mcgonagall as Harry knows her. He has a deep understanding of her from their time at Hogwarts, and if the fanfiction misses that, he won't like it.
One reason could be that he doesn't like others taking creative liberties with his story. He might feel that it's his story and only the original version should be the 'true' one.
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.
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.
One possible reason could be that Naruto's character development leads him to focus more on other aspects like his ninja duties or his bond with other friends. As he grows, his priorities shift.
Perhaps he likes to see how fans re - imagine his character. He might be curious about how others view his actions and motives throughout the story.
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.
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.
Maybe in the fanfiction, Naruto's positive and energetic personality attracts Ino more. He is always so full of life and has a big heart.
One reason could be that the fanfiction is set in a different universe where the characters' personalities are slightly altered. So, this 'new' Harry just doesn't click with Ginny in that version. For instance, if the fanfic is a darker take on the story, Harry might be more jaded and not open to a relationship with Ginny.