One possible reason could be Kakashi's strict teaching methods while not always following his own advice. For example, he might tell Naruto to always be on time for training but be late himself sometimes.
Perhaps Kakashi's attitude towards rules. He may enforce the village rules on Naruto and the others rigidly, but Naruto notices that Kakashi bends or breaks those rules in certain situations when it suits him. This disparity in behavior can lead Naruto to label him as a hypocrite.
Maybe Naruto is just teasing Neji. In the Naruto world, friends often playfully taunt each other. Naruto might have seen Neji do something that he thought was more like what a girl would do, like being overly cautious or having a particular grace in his movements. It could also be a random joke that Naruto came up with to get a reaction out of Neji.
It could also be due to a misunderstanding. Kakashi might be keeping some secrets from Naruto, like information about his parents or some hidden power within him. Naruto, being curious and eager for answers, could misinterpret Kakashi's motives for secrecy as a sign of distrust or dislike, which then turns into hatred.
He might be initially shocked. Since he sees himself as a good mentor, hearing such a harsh accusation from Naruto could leave him speechless for a moment.
One possible reason could be that Kakashi is preoccupied with other important matters in the village. Maybe he has some top - secret missions or tasks assigned by the Hokage that demand his full attention, leaving him with little time to focus on Naruto.
One possible reason could be that Naruto might feel Kakashi is too strict with his training. Maybe Kakashi's methods are too harsh for Naruto, making him frustrated and gradually developing dislike.
One possible reason could be Kakashi's reputation as a strict and powerful teacher. Naruto might be in awe of his skills and fear making mistakes in front of him.
One possible reason could be that Naruto might be trying to prove his independence. He has grown and wants to show that he can handle things on his own without always relying on Kakashi's guidance.
Perhaps he thinks fanfic undermines the integrity of the original Naruto story. The official story has a certain narrative and character development, and fanfic can deviate from that significantly. When it comes to his connection with Naruto, any deviation in fanfic might be seen as a negative. For example, if a fanfic changes the way he mentors Naruto, it could be something he wouldn't like.
One possible reason could be that in the fanfiction, Kakashi might have made a decision during a mission that Naruto strongly disagreed with. For example, Kakashi could have chosen to sacrifice something important to Naruto in order to achieve the overall mission objective.
In the fanfic, Kakashi might neglect Naruto's training due to a variety of reasons. He could be preoccupied with his own research or a secret mission that demands his full attention. There could also be a misunderstanding between him and Naruto. Maybe Naruto has done something that Kakashi misinterprets, causing him to distance himself from Naruto's training. Additionally, the fanfic could introduce new characters or plot elements that draw Kakashi's focus away from Naruto. For example, a new threat to the village that Kakashi feels he must handle alone, thus neglecting his duties as Naruto's trainer.