Culture Blind

''There is something strange about the composition of the German chaplaincy corps. I find among them chaplains of all faiths but no Jews.''

-American Pow interrogator in World War II.

Where a character displays a complete lack of understanding about culture, behaviour, social norms or other things that they should, by their own backstory and the world they live in, know. They don't have a plausible Fish Out of Water excuse like Time Travel into the past or future, or just arriving on a different planet, or even another country—they should know this stuff already. However, due to the Rule of Perception, if the audiences don't know about it, someone has to explain it.

What's particularly odd about these characters is that they tend to never really absorb much culture even in-show. It's almost a form of Negative Continuity to keep them stuck there.

Like Ping-Pong Naivete, except instead of back-and-forth, it's stalled completely except when the character's in front of a camera. The alternative to As You Know; since it's bizarrely "As You Don't Know." See also Genre Blind, which is similar to Culture Blind except that it extends to a character's entire reality.

May be used when Deliberate Values Dissonance would be far more plausible.

Of course, people like this do exist in Real Life, although probably not to the extreme degree that they do in fiction; some people, for whatever reason, just don't get out much, listen to the radio, or watch the news. In addition, people with Autism or Aspergers Syndrome may not understand acceptable forms of behaviour due to the very nature of their conditions.

Anime & Manga

 * Ash Ketchum from Pokémon knows surprisingly little about Pokémon, considering that the entire world is obsessed with them, and he's more obsessed with them than anybody else.
 * Naruto. At least Naruto himself is a dumbass, but one wonders exactly what they've been studying for years prior to the beginning of the show since every single thing needs to be explained.
 * Naruto didn't just skip classes, he put his ninja skills to use in order to escape in the middle of lessons. He also grew up as a social outcast. His lack of knowledge is actually partially justified.
 * Miaka from Fushigi Yugi. Sure, she traveled into the past to ancient China... but some of her actions can't even be justified using that as an excuse. One example that stands out is in the beginning, when she was with Tamahome watching the Emperor's procession in the city. Tamahome jokes that in exchange for his help, he wants her to get him a jewel off the Emperor's hat. She then actually proceeds to run up to the Emperor's palanquin, yelling for the Emperor to give her a jewel from his hat, and proceeds to grab at the palanquin and break part of it. And she acts shocked when the soldiers grab her and attempt to execute her. Think about it for a second in equivalent terms of a modern-day society: She runs up to the prime minister's car, grabbing at the car door and breaking parts of it, while screaming demands for the PM to give her ¥50,000. Miaka must have been living under a rock all her life, because no ordinary high school student (who supposedly gets high marks) would think (when not under the influence) that that would be a good idea.
 * In Hunter X Hunter, the first arc of the story has Gon and Killua understanding their world and culture just fine. And then the second arc comes... and all of a sudden, everyone except Gon and Killua know all about the techniques of Nen, Ren, Zen, etc. and have apparently known about it all along. So they end up having to start from the beginning, learning the basics and everything about it. It makes one wonder how in the world neither of them (who were actually considered strong in the first arc) were ever taught anything about it. It especially doesn't make sense in Killua's case, since he was supposed to come from a super powerful family of assassins.
 * Exists in Eyeshield 21, as the anime is about American football, something relatively unknown in Japan. One big example is a news reporter who came to the Devil Bats vs. White Knights game solely to cover athlete/model Haruto Sakuraba, and kept asking questions about how things worked. And on more than occasion an outsider has mistaken the game for rugby. Additionally, NASA Aliens receiver Jeremy Watt is an Occidental Otaku whose actual knowledge of Japanese language and culture is extremely limited, and often hilariously flawed.
 * The fact that it's set in Japan justifies a lot of the explanations given in the story. The commentators, for example, are mostly there to explain basic rules to the audience (in-story), who often mistake the game for rugby. Had the story taken place in America or been aimed at Americans, having to explain something as basic as "what is a touchdown" would seem downright insulting.
 * Jeremy Watt, however, is just a Cloudcuckoolander.
 * Gino Weinberg of Code Geass knows little about civilian life being a clueless nobleman.

Comics

 * Averted in Alley Oop. The titular caveman has been time traveling between his prehistoric world and the present day for years, and by now he is completely fluent in modern culture. This gets lampshaded whenever one of his caveman friends ends up time traveling with him and sees the modern world for the first time.
 * Characters in Chick tracts never know anything about Christianity (usually even being ignorant of Jesus or the religion itself), even if they're from countries that are overwhelmingly Christian.

Films -- Live Action

 * Mr. Miyagi of the Karate Kid movies is an example of this trope to an extent. In the first movie, having him use broken English was acceptable because we didn't get to learn very much about him beyond being the wise old Asian man who helps the main character learn self-confidence as well as self-defense. After learning in the second movie that he emigrated to the USA at the age of 18, 45 years earlier, his broken English makes quite a bit less sense.
 * Actually, the original Mr. Miyagi was an example, too. The man had been in America since at least the 1940s, as evidenced by his having served in a nisei regiment in Europe in World War Two (and receiving the Distinguished Service Cross). They also mention that his wife died in childbirth in one of the internment camps. (It's the scene where he shows Danny the difference between bonsai and banzai.)

Literature

 * A rather fatal example comes from the series The Tamuli by David Eddings. The church of Elenia continuously sends missionaries to the Rendors in order to try to convert them to their beliefs. Mind you, the Rendors aren't bad people, but they take their religion VERY seriously, and while they usually don't go around slaughtering nonbelievers, they are very easily angered, especially when it comes to religion. And unfortunately, the missionaries that the Elenes send tend to be the screaming zealot type, and go around ripping the veils off of women, and screaming that they're all heretics and damned to burn in hell. The end result is a small riot, and a lynched missionary, for very obvious reasons.
 * One knight, who had been assigned to be the bodyguard of a missionary that ended up this way, was asked why he didn't stop the crowd from lynching his charge. His reply is that he was supposed to protect the man from UNPROVOKED attacks, and when a man runs through the streets of a foreign city, ripping the veils off of women, and screaming out that they're all heretics, he's not only provoked them, but is obviously too stupid to risk himself and his men trying to save him.

Live Action TV

 * Classic example is Data from Star Trek: The Next Generation. Although his backstory has him serving in Starfleet for almost two decades after he was discovered and before he's assigned to the ship, apparently no one bothered to talk to him for all that time because it's only when he arrives on the Enterprise that he starts learning about things like aphorisms, clichés, common sayings, human social behaviour and the like.
 * Data, at least, was somewhat justified in the Expanded Universe; in the Prequel novel The Buried Age, Picard discovers him working as a records clerk in a backwater spacestation, where he's largely treated as a machine, not a person, so no-one does talk to him, except to make specific requests. (That still doesn't explain how he got through the Academy without ever hearing the phrase "wild goose chase", of course.)
 * Worf as well, should act as human as Riker. He's raised among humans, knows human values and ethics, but acts as if he's fresh off the boat from Quonos most of the time. While it doesn't excuse outright ignorance, a lot of his failing to fit in is implied to be overcompensation for just that. He is described as having spent much of his time growing up embracing his heritage and trying to be as Klingon as possible in Human society. That combined with his formantive years being among Klingons, makes it pretty reasonable. Guinan hangs a lampshade on this in one episode, telling him outright that most Klingons do not act as stiff and stoic as he does.
 * His stiff nature is itself lampshaded and explained in a later episode of Deep Space Nine, when he explains that as a youth living among humans, he accidentally killed another boy with a head-butt during a soccer match. It was accepted as an accident by everyone involved, but he realized how frail humans were compared to him and decided that to live among them, he had to always stay in control of himself.
 * Another example, although less blatant, is Brennan from Bones. Although she's focused primarily on her work, she displays a remarkable ignorance of current culture, which is odd given that she clearly wasn't always like that (she's a Wonder Woman fan, likes classic rock, but still has no idea what's in any movie or TV show released in the last 20 years).
 * The novels were eventually Justified. Apparently Brennan is so Culture Blind that she didn't realize people were reading her books for the sections of them that Angela wrote rather than her rigorous scientific accuracy.
 * Michael Scott from the American version of The Office could be this trope's poster child. His misunderstanding of other races and cultures is massive.
 * Sheldon Cooper in The Big Bang Theory. Although some of that could be because he's a) an example of Comedic Sociopathy and b) a long way along the Asperger Syndrome Diagnostic Scale,

Web Comics

 * Riff from Sluggy Freelance apparently didn't know that people get weekends off from work. It's somewhat justified since he had never worked a 9-to-5 job before, but even so that seems like something he should have picked up from TV or something.
 * Much like Ash, Atticus from the Pokémon fancomic Moképon is generally clueless about how his world works. In his case, however, it's because he simply never cared about the whole "amazing, life-changing adventures and friendships" that his world revolves around.

Western Animation

 * In Mulan II, Mulan is shocked when she hears that three princesses have been betrothed in an arranged marriage. This shouldn't surprise her, as it is most likely one of the most normal things in the world where and when she lives, and her own marriage to Shang for love is probably a huge exception.
 * Especially considering that the first film begins with Mulan flubbing her meeting with the Matchmaker in an attempt to get an arranged marriage herself. That's why fans don't really talk about the sequel.