Quote Originally Posted by Blizzard's In-Game Code of Conduct
Hate speech and discriminatory language is inappropriate, as is any obscene or disruptive language. Threatening or harassing another player is always unacceptable, regardless of language used. Violating any of these expectations will result in account restrictions. More serious and repeated violations will result in greater restrictions.
We are more lax on people calling each other idiots, morons, etc because in a game where critical thinking is key we all have moments where we are genuine morons. It would be nice if people could control their emotions and be decent to each other, but I understand in the moment we all do/say things we normally wouldn't. That understanding has no room for people that take it too far though. Racism, bigotry, homphobia, etc are not welcome at all.

It's situational though. If someone is hounding someone else with "light" insults it starts to become griefing territory.