A joke that's only funny if you're familiar with a certain subject
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"Um... that, that was funny... if you um, if you studied Taglarin mythic rites... and are a complete dork."The trick to telling a good joke is to ensure that the basic subject of the joke is something that the average person would be familiar with. Therefore, in fiction-land, a good source of humor (for the audience anyway) is to have someone tell a joke that would only be understood by people with a specific area of expertise, then watch as the joke goes unappreciated by their friends, who lack the knowledge necessary to grasp the humour. This trope generally manifests itself as a forced effort to be funny by a character not normally known for their jokes. As such it may be typical of the Hollywood Nerd. May overlap with Genius Bonus and Viewers Are Geniuses, although it can be distinguished by one or more characters in the story also failing to get the joke.
-- Tara McClay, Buffy the Vampire Slayer, "Family"