If your only exposure to the various books in the X-Men line is the Uncanny X-Cast podcast, you'd get the impression that it's just accepted that X-Force (vol. 3) was the only consistently good book in the line, X Factor is entirely useless, and Greg Land is a wonderful artist. Start with certain other online reviewers and you'll come away with the impression that it's a universally accepted, scientifically proven fact that X-Force (vol. 3) was rubbish and X Factor is the only Xbook worth reading, and that it's literally impossible NOT to believe that blindness would be preferable to having to look at Greg Land's art. It's not that both sides disagree, it's that they seem completely unaware that anyone in the world holds the other opinion.
Reactions of older readers for DC Comics' New 52 relaunch are getting this as well; many are still in shock that people are enjoying anything coming out of it.
A lot of famous movies hailed as classics, such as Jurassic Park and Forrest Gump did more poorly with critics than one would expect. They still did good, but it wasn't all acclaim. As an example, Forrest Gump's tomatometer is only 71%, and both it and Jurassic Park only have an average rating of 7 out of 10.
With movies that have multiple cuts and director's cuts, many fans automatically prefer the director's cut simply because it's marketed as the "film presented in the way the director intended". They will often regard the original release as inferior even if it's the release that they originally loved for decades, ignorant of the existence of a director's cut. Such fans will often dismiss those who stick to the cut that they "loved growing up", regarding them as improperly viewing the movie through a Nostalgia Filter.
With Star Wars, it seems the inverse is happening; most fans view the original release of the original trilogy as superior to all the revisionary cuts that came after it.
Harry Potter: Potterheads, if you're going to study English in college, be prepared — they diss Rowling all the time there. Some creative writing classes devote entire lessons to teaching pupils not to put the books on a pedestal. Same goes for other popular and well-loved books.
The Da Vinci Code: Two sides. One, "holy crap, how do people actually like this trash?!" and two, "Wait a minute, I thought it was a good book!"
People who talk about what is and what isn't 'real music' or how 'there isn't any good music anymore'. If someone has heard examples of a genre that they dislike they will automatically write off the whole genre as bad and 'how can anybody listen to it?'
In a similar manner, don't tell certain vinyl collectors (the kind who collect old, rare records merely to put on display) about how you listen to your records. Expect a massive diatribe if you casually mention you opened a sealed record.
People who refuse to share rare music on the grounds that they have something hardly anyone has are like this. Especially when someone else shares their copy of the same material and says they're doing it because they want to make people happy.
The director's cut example mentioned for films also applied when the British versions of the early Beatles albums were released on CD in the US in The Eighties. Most fans embraced them and they gained retroactive status as the official Beatles discography. But there was enough nostalgia for the original US Capitol Records releases that the LPs and cassettes circulated widely among collectors. As a result Capitol released two deluxe CD box sets of the US albums, only to get bashed by purists accusing them of greed and peddling inferior mixes of the music.
This is one of the main reasons that the Television Without Pity forums maintain strict "no talking about the boards on the board" and "Talk about the posts, not the other posters" policies. Posts like "I don't get why everybody wants her to win" or "What's wrong with all these people who don't like him?" will net at least a warning and possibly a ban.
This overlaps often with Critical Dissonance. Many reviewers, especially Video Game reviewers, seem to think that because their tastes are limited, that means that any game they review should be strictly along those.
A very notable example are the reviews of Grand Theft Auto IV, which gushed about recreating a living, breathing world, while minimizing the gameplay and technical issues, which were noted strongly in user reviews.
A common form is if they think the content of a game is "kiddie", they will put that well above if the gameplay is any good, how the game performs, replay value, and other factors that would appeal to many gamers more than whether a game is kiddie or not. Because they don't like kiddie games, it's clear no one else will.
Players also respond to video game reviews (seemingly more so than other forms of reviews) especially strongly in this way. Expect any review of a video game that disagrees with someone's opinions to be met with numerous comments about how the person/the site is biased and that reviews should be objective, even though an objective review is impossible; any criteria or theory you choose to follow in a review is in and of itself a form of bias. This is what an objective and unbiased review looks like.
One game reviewer talked about this, stating more or less, what while most reviewers talk about what the game is, what you do, and why they thought it was fun, a truly good reviewer also talks about why you the reader might like it.
Browse Facebook fan pages. While you'll find a lot of posts about how good a work is or gushing about certain characters, you'll invariably get haters of the work liking the page simply to say, "How can you people like this crap?" or "You people are stupid, [Work] is obviously bad!" Some more extreme haters will demand the page get deleted because it dares to like something they don't. Similarly, browse pages devoted to hating certain works and you'll find the same thing in reverse: fans posting on the page saying, "You people are stupid!", "You obviously don't realise how superior [Work] is!", or "You just haven't read/watched it!", and some demanding that the page get taken down because it dares to not like something they do.
Shipping wars. So many vicious, seething, blood-boiling wars have been launched because so many fans could not comprehend how anyone could not support their One True Pairing. Not even fans who don't ship them with anyone or have no interest in shipping will be spared, because shippers believe that their OTP champions true everlasting love and if you don't agree with them, then you must not believe in love.
The comparisons of earlier works to newer, updated, or reimagined versions. Those who stick by the earlier works and admit they were enjoyable are often accused of wearing a Nostalgia Filter. At the same time, those who prefer the newer versions are accused of not understanding what made the original compelling in the first place or only capable of liking newer productions simply because they are more recent and made on better budgets with newer technology (especially CGI effects).
The Internet Wrestling Community, or the IWC. As a whole, they tend to favor wrestlers with a higher "workrate." At times, this tends to conflict with who's actually over and receiving a push in various promotions.
The general feedback loop of "Oh my God, grown men like My Little Pony now?!"/"Yeah, we like My Little Pony now, what are you gonna do about it?" has led many bronies to forget that the show has just as many fans in its target demographic (that is, small children, especially of the female variety) as it does grown men and women, which occasionally causes friction when people who haven't forgotten this ask them to try and make their... not quitework safe material a little less accessible for the young'uns. Which has apparently led to the newly-penned "Brony Pledge", which is less a "pledge" and more of a "stern reminder from one of us to the rest of you". Which, admittedly, is in and of itself rather more decorum than one usually sees from fandoms that have an excess of Rule 34.
Animation vet Bruce Timm has said that he rarely lets internet criticism get to him for precisely this reason. He reasoned that statistically speaking, the people who post on message boards are a very small fraction of the actual fandom and audience, so just because some people are screaming Ruined Forever!, that doesn't make it representative of the general opinion of his work.
Anyone who spends five minutes on a comic book message board would think Ultimate Spider-Man is the most hated cartoon of all time, when in reality, it does quite well among its target demographic of young children. Brian Bendis pointed out that even though "It's for kids!" is a common admission of a lack of quality, the network and advertisers don't actually care what the small Periphery Demographic of grown men think. In the United States at least, kids are still the primary consumers of superhero animation and the tie-in toys, so anyone is else pretty much irrelevant as far as the execs are concerned.