Question

you notice that your best friend often picks up quarrels with jonior students in the school bus you feel that most time es unreasonable

Answer 1

perhaps this same thing has happened to him when he was a junior. or perhaps he thinks it is cool.tell him that most of the time he is unreasonable. and this may lead people to think that he is unnecessarily rude and would start to ignore him

Answer 2

It may be coz he must had faced the same situation in his younger age. I would tell him that this is not a good thing and its also rude. Being so rude with his juniors and most of the times even unreasonable can effect his own image. So, I would probably stop him from doing that.