That Sounds Familiar

A corruption or misuse of a word or phrase by people who have obviously heard it used, but understand the concept very loosely and have no idea of its origins. This can be Played for Laughs, with the comedy coming from the audience understanding the original significance of the word. Alternatively, the original term might be very significant, powerful or evil but its misuse is incongruously trivial. Finally, it might be insignificant and simply used to set a scene as being related to the real world, or as a throwaway gag when the setting is clearly alien.

Often used in Future Imperfect settings, where the borrowers of the term are the descendants of the originators.

Film

 * The Nightmare Before Christmas has Sandy Claws.
 * In the Planet of the Apes remake, the holy site Calima's name was taken from a partially-covered "Caution Live Animals" sign on the ship.
 * In the first Star Trek movie, V'Ger started out as the Voyager probe.
 * In turn, parodied by a Codename: Kids Next Door ep, where Ramon-4 started out as an ill-fated Rainbow Monkeys project (the 4 coming from "4Ever").
 * In Zardoz, the name of the eponymous "god" is a deliberate corruption of

Literature

 * In the Harry Potter series, the phrase Avada Kedavra is the incantation to possibly the most powerful curse known to the wizarding world. Muggles, on the other hand, know Abra Kadabra as a nonsense "magic word" used by stage magicians. It is implied that the sheer power of the word has allowed it to filter through The Masquerade.
 * Actually, "abracadabra" dates back to at least the 2nd century as a magical word of power inscribed on healing amulets. It's based on a semitic language in which "ibra" means "I create" and "k'dibra" means "by speaking it".
 * The Hitchhiker's Guide to the Galaxy has a couple of these:
 * One of the reasons for Earth being shunned by the rest of civilisation is that it took the Genetic Memory of the devastating Krikkit Wars and turned it into a rather dull spectator sport.
 * Every species in the galaxy has some drink whose name is a variation on Gin and Tonic, which has confused etymologists for centuries. The drinks are all completely different; it's just the name that is identical. Variations listed include jynnan tonnyx, jinond-o-nicks, chinanto nigs, txjin-anthonty-ks, and of course, the Terran gin and tonic.
 * The word Belgium is considered the most obscene profanity in the galaxy. The casual use of the word is considered a shock to most cultured beings. One of the other reasons humanity is shunned is that we use that word far too casually for the galaxy's tender sensibilities.
 * Several of the place-names in Carpet People are obvious corruptions of the human artifacts they are based around, such as "Achairleg" and "On Epen Ny".
 * Another Terry Pratchett example would be Inn Sewer Ants and Den Chewers.
 * Mr. Tumnus thinking that the Pevensies came from "War Drobe" in the country of "Spare Oom".
 * In the fantasy trilogy "Water", the Atlanteans have a magic sword called Eikiss Cali Werr.
 * The Indian in the Cupboard has Little Bear thinking that he and the other Living Toys come from something called "plaz-tek".
 * In Lord of the Rings, Frodo sings an ancient hobbit tune that the narrator notes only survives in fragments today. The verses that are familiar to readers are clearly from the nursery rhyme "Hey Diddle Diddle".
 * Winnie the Pooh: Piglet takes an incomplete "Trespassers Will Be Prosecuted" sign to be the name of his grandfather, Trespassers William.
 * "Magic City" may be the ur example of this. A novelette written in 1943, it featured a post apocalyptic world with people reciting prayers off of signs they read like "O left tur" and "O parki". The country was called Tizathy ... as in "My country, tizathy, sweet land of liberty..."
 * The After the End community in Gathering Blue, the sort-of sequel to The Giver, has an annual tradition involving a song whose lyrics are chopped-up names of current cities. The people no longer know what they mean.
 * In Un Lun Dun is absolutely full of these- not surprising, since the title of the book is "Un-London".
 * In the Army of the Sun trilogy, aliens refer to humans as "ersers". Subverted in that they know exactly where the term comes from.
 * In Neverwhere, we are the ones doing this, with the names of places in London Above being vague and often corrupted shadows describing things in London Below, such as "The Angel, Islington" really referring to an Angel called Islington.
 * The Star Trek Expanded Universe book The Sundered has this with an apparently alien race called the Neyel, who turn out to be a long-lost offshoot of humanity from the vanished O'Neill asteroid colony, who adopted Bio Augmentation to the point that they no longer look human. Many of their terms fall into this category, such as their word for captain or leader, drech'tor, which comes from 'director'.

Live Action TV

 * In the Star Trek: The Original Series episode "The Omega Glory", the inhabitants of an inexplicably Earthlike planet retain several of the founding documents of the United States of America, but mispronounce the words—for example, they read the Preamble to the U.S. Constitution as "Eee Plebnista, norcom, forcom, perfectumum..."—and blindly venerate the documents as "holy" without understanding what they mean.
 * Doctor Who has Leela, a member of the Sevateem, which is a corruption of "Survey Team". The Sevateem were at war with the Tesh (the Technicians).

Video Games

 * The Fallout games have several settlements whose names are apparently derived from corrupted names and degraded signage:
 * Fallout3 has the town of Arefu, whose name comes from a traffic sign hanging over heard reading "Careful" with the first and last letters worn out; Andale, an apparent reference to the real life town of Annandale and "The Pitt", located in the remains of Pittsburg.
 * Fallout: New Vegas has Novac, named after a malfuctioning "NO VACancy" motel sign and "Freeside", located in what used to be Fremont Street. The Old World Blues DLC is centered around a scientific research facility named "Big Mountain", commonly abbreviated as "Big MT". The corruption of the name, coupled with its secluded location and the fact that people who tried exploring the crater tended to not come back led to it being known as "The Big Empty" in the Mojave Wasteland.

Web Comics

 * In an Intragalactic strip, Captain Benjamin tells the story behind Joelmas, which is a corruption of the plot of Mystery Science Theater 3000.

Western Animation

 * Futurama parodies Star Trek's V'Ger with VGINY (the name enlicits a chuckle from Fry whenever it is mentioned)