Let me start off by saying I've been muted a couple of times now.
First by yelling "fuck chinese gold sellers" in Ironforge during the related apocalypse. Justified I feel.
Second one was mentioning that I like chinese mages, I've met a quite a few and they all deny a tip for water and food.
Third one was today. I asked Vivalacartel for the price of the Devilsaur set, he said 410 gold. I told him I would take it for free or I would kill him in Un'goro. The sentence contained "i will kill you" and I imagine this is what triggered it, since I was instantly muted after that.
Be careful what you write, the system is really sensitive...