OKAY PERSONAL OPINION INC
It annoys me when, during the course of an evening of Warcraft, someone tries to support their (false) argument with 'Well I played in (some sort of) beta,' as though playing the beta automagically makes you insanely knowledgable about the current state of the game. This, to me, is a lot like me saying that I know everything about driving a car because I have driven for so many hours around and around my driveway and/or nearest parking lot.
I don't know a lot about driving (though I know more than I did a year ago for certainly).
But I do know a WHOLE LOT about Warcraft (although I do on occasion forget something, such as the precise level range for Uldaman), and it annoys me when people try to undermine my correct statement of facts by saying that they have been playing longer than I have. When I am describing the proper strategems for winning such and such Battlegrounds (a thing that did not even EXIST during beta) or such and such boss (again, many of which now also did NOT EXIST during beta) and my line of reasoning, which is based on empirical evidence and more experience than is really necessary to mention (on account of it is sad and embarrassing), I hate this as a counter argument.
Like it or not, the way I've played Wow for the past year + has been on a sub-professional level. Not professional, cos I'm not member of Death and Taxes or anything nutty like that, nor am I my twin brother (who knows more about the game than should be legal for any single person), but certainly I have logged enough hours with nearly every currently available experience that you can trust my opinion on it to be true MOST of the time. I say most because I in my inevitable fallibility can mix up / forget a fact, but if I am telling you what to do, you can usually trust that I am not leading you astray. Unless I hate you.
The other thing I hate is when people take my dissemination of information as belittling or demeaning to themselves. I'm usually achingly polite to people I don't know. As an example, in a recent Alterac Valley, I was growing frustrated. Most of the Stormpike forces were advancing towards the Frostwolf village and leaving our back exposed for good solid knifing. I remained behind to protect the captain and the holdings surrounding her, and encouraged a small contingent of players to do the same, because if everything is held by your side and your captain is alive when the game is finished, you receive a great deal more honor and reputation. When I tried to explain that it would be to our benefit to keep the rear intact, the self appointed raid leader of that game became quite surly with me and accused me of being a 'zergling.' I politely explained my logic and asked him to find fault with it, which he could not. He did apologize post game (which we won, and which netted the winning players mass honor because some of em DID listen to me), but the point is that I didn't return with any name calling or saying he is a nub or whatever, merely explained my reasoning and assured him that I was acting in the best interest of everyone there.
Not that I'm altruistic, exactly. I don't need the rep (I'm exalted) or the honor. I just hate to lose.
It's true that part of a game's object is to have fun. But the other part is to win, and I find it fun to win, especially when said win is ruthless in its perfection. When I make a comment or a suggestion, it is only ever to help this win happen. It's not meant to make anyone feel stupid or to usurp any sort of imagined power structure.