I think what winds me up so much about a few of the folks on the could be summed up by two main points (though they are prob two sides of the same coin): (a) the way they make listening to, discussing and evaluating music all about them, making each new kind of music just the next little chapter in their self-enclosed narrative of development as a music listener and (b) their extreme sense of entitlement, the way they expect all music to come to them and fit perfectly with their preformed ideal categories before it is worthy of any engagement at all.
In fairness, I suppose I ought to bear in mind that a fair few of them are actually professional music critics/journalists and that cynical, weary attitudes like that are liable to come with the territory if you've been involved in the music industry for a long time.
Having said all this I am now going to go back to concentrating on the positives as usual, because I find that more productive. I guess it's a lesson never to take anything on internet message-boards too seriously (though I should point out that I never think about these things when I'm offline anyway).