I hate that so much. It makes me wish I could reach out and punch that player in the face really, really hard. It's actually one of the reasons I don't play MMOs very often. I can only tolerate other players rudeness in small doses.
I also hate it when players send me a group invite without whispering me first. It's very jarring to be fighting some mobs when suddenly a box just pops up on the screen blocking my view. Makes me curse silently every time.