A tank from Mal'ganis tried to kick me for being the ~wrong~ spec once (I was Arcane, how dare I not be Frost). Three minutes into a Gnomeregan run he goes "Why is this mage Arcane?" in /instance, insulting me and threatening to kick me until I just put him on ignore.

At that level Frost's got...what, Frostbolt, Ice Lance and Frostfire Bolt to work with in terms of DPS? Not really mind-blowing, so I don't know what the big deal was.