He did not hate him at first, he took him as his diciple etc. But Meng Yao killed his officer (I think it was somone pretty important, like Nie Migjue's right hand man). That made NMJ angry, but he didin't really punish him, just make him leave the sect. Then Meng Yao joined the Wens and when NMJ was captured MJ killed the soldiers he had with him and threatened him etc. MY did this in order to gain Wen's trust, as he was a spy, but NMJ didn't know this and even after he learned about this he still suspected his bad intentions, becouse of this erlier killed generall. And he always blamed MY for the life of those Nie soldiers that died by MY hands. He the became distrustfull towards MY actions. But he still agreed to the sworn brotherhood beatwean them, probably in hope of rightening MY. He thought that MY is making a mistake while working for the Jin's. My always was trying to pleas his father, which also angered NMJ, becouse he was doing it instead of doing the right thing. Like for example MY insisted to not kill Xue Yang, becouse that was what MY's father wanted. NMJ was more distrusting him, then actually hating him. Later on his negative feeling was amplified by MY music, and he was close to Q deviation, so it was way easier for him to get angry at little things.

@@Makjaoiuewhxkjs thx

I've heard people theorize that it's to make him seem taller, since he's the shortest named male character.

His mother told him gentlemen wear that style of hat