Are you bored with the usual holidays? How about celebrating a new holiday!

This trope deals with holidays non-existent in the real world, in other words holidays that only exist in a story's universe.

Just about any fictional fantasy setting with their own fantasy nations/history/cultures will come with their own fictional holidays. Sister Trope to YouMeanXmas.
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!!Holidays existent in-universe:
* ''AnimalCrossing'' has a bunch of holidays that are either made-up (Yay Day, La-Di-Day, Bright Lights, Festivale) or JonasQuinn holidays (Toy Day ((Christmas)), Bunny Day ((Easter)), etc).
* Winter-Een-Mass in ''CtrlAltDel''.
* ''{{Quark}}'': Happy Number 11!
* Whacking Day in ''TheSimpsons''.
* Clam Day in ''FamilyGuy''.
* In ''[=~The Adventures of Dr. McNinja~=]'', Dr. [=McNinja=] and his family celebrate "Katanaka", which commemorates their irish ancestors' original victory over pirates. It's observed on Thanksgiving so they can get off work too.
* ''{{Dinosaurs}}'' had "Refrigerator Day", and expy/parody of Christmas.
* ''{{Kingdom of Loathing}}'' uses a mixture of real-world and fictional holidays, to go with its fictional calendar: The Festival of Jarlsberg (New Years Day), St. Sneaky Pete's Day (St. Patrick's Day), Oyster Egg Day (Easter), Generic Summer Holiday (Summer Break, more or less, rather than any specific day), Dependence Day (Fourth of July aka Independence Day), and Crimbo (Christmas) circulate around the calendar along with real-world holidays like Valentines Day and Halloween. Border-line cases such as Labór Day and Arrrrbor Day also exist.
* An episode of ''{{Daria}}'', widely considered DisContinuity at the time, had the eponomous character run into anthromorphic holidays - including Valentines Day, St. Patty's Day, Halloween, and Guy Fawkes Day. As it was primarily an American (MTV, at that) series, most viewers probably thought the last one was fictional. It's not.
* Life Day in TheStarWarsHolidaySpecial.
* Colonial Day in the re-imagined ''BattlestarGalactica''.
* Festivus in ''{{Seinfeld}}''.
** Actually, Festivus is ''real''! Come on, everyone, let's decorate the pole! We're done!
* The Day of the Dead (Brakiri holiday, not Mexican) in ''{{Babylon 5}}''.
* ''HomestarRunner'' likes to refer to Christmas and Thanksgiving as Decemberween and Novemberween, respectively.
*Rose Nylund from ''TheGoldenGirls'' reminisces about St. Olaf holidays: Everybody Hide the Corn Day, Hay Day, the Day of the Princess Pig, and the Day of the Wheat, when everybody came to town dressed as sandwiches.
*Vivian Stanshall, ''Sir Henry at Rawlinson End'' (album and film versions): "To celebrate All Squids' Day there was a face-jumping competition at the Fool and Bladder."
*''StarTrekTheOriginalSeries'' episode "The Return of the Archons". The planet Beta 3 had the holiday called Festival, in which the population went totally berserk (destroying, raping, etc.) for 1 hour (the "Red Hour"), then returned to their normal placid demeanor. This was due to their mental conditioning by the computer Landru.
*''{{Traveller}} Classic''. The Imperium in general had the Emperor's Birthday. One planet had a three day holiday during which the local law level was reduced to zero (i.e. no laws at all) to let the population blow off steam.
*An issue of the ''{{ALF}}'' comic book revealed that Melmac had a variety of holidays.
** Shown inside are:
***Eat Off The Floor Day, in which celebrants (are supposed to) dress in bathing suits and eat "duck delight" while sitting on the floor, celebrating the discovery of linoleum by Alexander Graham Cracker. The foodstuff is not made of duck, but makes those who eat it think they're ducks. The two adult Tanners sample it early and go quackers.
***Wear A Plant Day, in which a tree is planted that is supposed to grow to about a meter in height by evening. It gets nixed immediately by Willie, who discards the seed. A chance raccoon, however, knocks over the can, planting the seed... which begins to grow at an astonishing rate, due to Earth's relatively rich soil. Within the hour, it threatens to start a forest in the backyard that will spread from there in California to the Mississippi River by Thursday.
**Shown on the front cover and mentioned within are: Bathe With A Policeman Day, Goomer's Birthday, UPC Symbol Day, Eat Your Calendar Day (which appears to be when cover was made, judging by Gordon's activities), Sit On A Friend Day, Play With Your Spaghetti Day, Give A Present To A Wall Day, Wear A Banana Split Day, Yad Sdrawkcab Gnihtyreve Lleps... and Make Up Your Own Holiday Day.
* ''TenchiMuyo'' has the Juraian holiday Startica, which happens to involve Christmas trees for some reason.
* Clearance Day in ''SheepInTheBigCity''.
* ''UndocumentedFeatures'' gave us such delightful Dantrovian holidays as "The Festival of the Fudge Sauce", "Terzayyl", and "The Day The Colonists From Earth Finally Understood"....
*Bobunk in ''SabrinaTheTeenageWitch''. It's too bad that Salem accidentally deleted it...
* "Heaven's Day" in ''TheBigO'' Anime, which was the day Paradigm City was founded. It's clearly related to Christmas (giving presents, trees, etc.)
* The calendar is littered with official days declared by the government, but you don't get to stay home. One that's been in the news recently has been National Nude Hiking Day, which coincided with Governor Sanford's purported hike down the Appalachian trail. I bet every day mentioned on this page will have been silently codified by a fan in some city council somewhere.
*TalkLikeAPirateDay.
* In ''SpongebobSquarepants'', No Spongebob Day.
** Adding to the Spongebob thing, Leif Erikson Day. Also the Narrator mentions that every day for Spongebob is a holiday. (Even if he has to make one up - though not in the case of Leif Erikson Day, which is a real holiday).
* This Troper has seen ads for MagicTheGathering Pro Tour dates and there were often fake holidays on the calendars. This troper can't remember the names, though.
*Weasel Stomping Day, a holiday created (in a sense) by WeirdAlYankovic in a song detailing a holiday held where people spend the day using large boots to crush weasels.
* FairlyOddparents. Timmy's alien friend celebrates FLARG, which culminates in him blowing up Earth.

!!Holidays Made Up By A Character:
* ''{{Doug}}'' has a subversion to it. Doug imagines his alter ego Captain Quail fighting a villain who wants to get rid of the weekdays. In the end, not only does he foil his plans, but creates a whole new weekday known as Funday in the process.
* In ''{{Doraemon}}'', Nobita uses one of Doraemon's magical gadgets to declare "Do Nothing Day". HilarityEnsues.
* In The O.C., Seth's family celebrates "Christmukah," a combination of Christmas and Hannukah.
* In ''{{Futurama}}'', Bender made up Robanuka as an excuse for not working. The characters later decide to actually celebrate it - by "doing the robot dance", with Jewish music playing in the background.
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<<|HolidayTropes|>>