I have a friend since H.S. and we have spent a lot of time playing games together. We recently got back into WoW after seeing the changes coming to Legion. After the movie release I have seen old friends come back into the game as well as completely new players eager to play the game, this is when I realized that my friend is the type of WoW player that I hope no one runs into. He basically makes fun of people with terrible transmog, lower level gear while having the legendary ring, and those riding common mounts. Earlier today he saw a character with level boosted gear on walking around Lion's watch, he then proceeded to /spit on the character and told me he's spitting on him because he's "boosted" #POGCHAMP!. He's a friend so I want to help him change, what can I do to help him stop his harassing ways? Sorry for grammar and word choices, English isn't my first language.

tldr: friend is a twat to other players, need help to change him.