One of my biggest pet-peeves is people who take the joy out of knitting through their complaints or by saying, "You can't do it that way, it doesn't work and it's not the RIGHT way to do it."
The first group of people are the ones who pick out and knit a pattern, and when they're done criticize it not in any constructive way, but for all the things that make it that pattern. If they knit the Jaywalker socks, they might complain that they're too stripey or that chevrons are ugly. If they knit a Clapotis, it would be too ruffly and they can't imagine that the designer possibly thought this through all the way. That kind of criticism is absolutely pointless, but if the person saying it is a well-respected blogger, it can cause needless damage to the pattern designer's reputation as all the people who read the blog come away with the impression that there's something wrong with the design, when in reality there's something wrong with the blogger's expectation.
There's nothing wrong with legitimate criticism, and I have no problem with someone commenting that the pattern had a lot of errata in it, or that it would make more sense to do this step before that one, etc. That's useful information, as it helps the designer create a better pattern next time. But it's ridiculous for you to choose a pattern to knit out of the thousands that are available on Ravelry, and then lambaste it for the things that make it that pattern and not any other one.
The other group of people are the knitting police, who think that their way is the only or the best way. The awesome thing about knitting is that as long as you're happy with the end result you get, then you did it "the right way." There are always different techniques to learn, but that's all they are - different. You might decide that they are better in particular instances, but in no way is any technique inherently better than another one if you prefer the result the other one gives you. For example, I've read and been told repeatedly that casting on over two needles to get a stretchy cast-on is dumb, and that it doesn't actually give you a strechier cast-on. But every time I do it, I get a stretchier cast-on. So even though the knitting police tell me that it's "wrong," I'm going to continue to do it, because I'm happy with the result it produces.
I guess the reason both of these types of people bother me is that they both seem to assume that their view is right, and that people who don't adhere to the same view are wrong and somehow less because of it, and that bothers me. Knitting is about sharing joy, not making people feel bad for not doing it the same way you do.