I've got a good one:
Whenever you browse the internet, forums etc, in search of advice on subject x, y, or z, what the best product is in a certain field/hobby, etc, in order to make a purchase down the line, or do some research. Hell, maybe you even ask the question yourself.
And instead of receiving advice from those morec knowledgeable than yourself, you get some smarmy dickhead, narc know it all who responds something like:
'The best 'x' is the one you really like,'
Or maybe it's
'Nobody can tell you which one is the best for YOU.'
Instead of providing helpful advice, these smug asshole oxygen thieves have just managed to write a bunch of nothing, saying nothing, and wasted everyone's time. Why not just dispense with some useful knowhow or recommendation instead of being a black hole of aphorisms and half wit comments?
That's right, because they may not even fucking know anything about the topic in question.
Funnily enough, these are usually the kind of dunces who will tell you to 'use the search function, this question has been asked before.'
The last time it was asked? 'Thread last updated Oct. 2 2007 12:03.'
I'm obviously talking about Reddit mainly, but I've encountered these people since the early 2000s on various BBS.