* ActorAllusion: In "Sweet Dee has a Heart Attack", Frank escapes a mental institution in the same manner as Chief Broom in ''Film/OneFlewOverTheCuckoosNest''. Danny [=DeVito=] played a minor character in that movie.
** In "Dennis and Sweet Dee's Mom Is Dead," Dennis and Dee's natural father Bruce mentions that he is a minister; Stephen Collins, who plays Bruce, was a pastor in his best-known role on ''Series/SeventhHeaven''. However, see FunnyAneurysm =Moment and NiceCharacterMeanActor below.
** In "Charlie has Cancer" Dee tells her friend Artemis that the bar has a {{Coyote Ugly}} thing going on. Kaitlin Olson had a very brief appearance in the film
* ChannelHop: In an effort to attract interest in the launch of [=FX=]'s comedy-oriented spinoff channel [=FXX=], ''Sunny'' was moved to the new channel along with ''Series/TheLeague'' and ''Series/{{Legit}}''.
* TheDanza: Charlie Kelly is played by Charlie Day, Mac is played by Rob [=McElhenny=], and recurring character Artemis is played by Artemis Pebdani. Specifically averted by Dennis: Glenn Howerton did not want his real name associated so closely with the character.
* {{Defictionalization}}:
** Those dick towels they were trying to market? You can buy them, but don't Google them if you're on a shared home computer or on a computer in a public setting (read: library, computer lab at school, etc).
** Greenman, which has not only been defictionalized, but is well on its way to cultural phenomenon status.
** Recipes for "milk steak", a dish Charlie apparently made up in "The Waitress Is Getting Married", have appeared online.
** And now fans have done the same for Rum Ham (not to be confused with an existing recipe for wussy, rum-glazed ham). It tastes pretty awful, but it'll get you good and wasted.
* DyeingForYourArt: Rob [=McElhenney=] gained ''50 pounds'' in order to prove a point about sitcoms for season 7.
* ExecutiveMeddling: A story involving The Gang getting onto ''GameShow/FamilyFeud'' was ultimately vetoed by FX, despite the support of ''Feud'''s producers.
* ExiledFromContinuity: Averted; Creator/RobMcElhenney got the idea for Charlie's "Green Man" persona from an unnamed friend, who donned a green zentai suit while attending a football game with [=McElhenney=]. [=McElhenney=] would later pay his friend an undisclosed amount of money in exchange for the rights to his "character", so that he could use the concept in later episodes.
* FunnyAneurysmMoment: Stephen Collins plays the altruistic biological father of Dennis and Dee, who is active in children's charities and adopted a dozen African orphans. In 2014, Collins was recorded confessing to the molestation of multiple children.
* [[IronyAsSheIsCast Irony as They Are Cast]]: The cast members usually have some irony going for them:
** Mac is portrayed as an ArmoredClosetGay who uses homophobia in a flimsy attempt to deny his own homosexuality. Rob [=McElhenney=] [[HasTwoMommies was raised by a lesbian couple]].
** Charlie is a StalkerWithACrush on [[NoNameGiven The Waitress]], much to her displeasure. Charlie Day and Mary Elizabeth Ellis are HappilyMarried and have a child.
** Dennis is a sociopathic, vain narcissist whose self-worth outweighs any actual intelligence. Glenn Howerton [[HiddenDepths is fluent in Korean, Mandarin, Japanese and French, and considered a career in Aerospace Engineering before deciding to go into acting]].
** Dee is the resident ButtMonkey of the group and is constantly abused by everyone. Katlin Olson is married to Rob, the show's creator.
*** Even more ironic, there's two scenes where Dee and Mac have to pretend to be into each other and act very unconvincingly. One time, they act out a {{Sitcom}} "WillTheyOrWontThey" subplot to help popularize their bar. It ended in a fight where Mac strangles her. Another time, Dee plays the LoveInterest of Mac's character in a film which worked out fine until they had to kiss.
** Frank is portrayed as a [[TheHedonist wild, depraved man]] with a devil-may-care attitude towards everything. Creator/DannyDeVito is far more stable in real life.
* {{Jossed}}: A fan theory is that [[EveryoneCallsHimBarkeep The Waitress]]'s name is Nikki Potnick because she couldn't find her name tag at her high school reunion and Frank had stolen the "Nikki Potnick" tag. During his "Ask Me Anything" for Reddit, Glenn Howerton said in no uncertain terms that "the Waitress is NOT Nikki Potnick."
* MeanCharacterNiceActor: The main cast kind of have to be this trope, [[UnsympatheticComedyProtagonist given]] [[ComedicSociopathy who]] [[{{Jerkass}} they]] [[LoserProtagonist have]] [[SmallNameBigEgo to]] [[VillainProtagonist play]]. Special mention goes to Glenn Howerton, who finds Dennis to be such a repulsive psychopath that he opted out of being TheDanza like Charlie and Rob, not wanted to be too associated with someone like Dennis.
** NiceCharacterMeanActor: Stephen Collins, who played Bruce Mathis? [[PaedoHunt well]], see FunnyAneurysmMoment above.
* NoBudget: The show's first season was produced at 1/3 of a typical network sitcom's budget, starred unknown actors and during production, Rob [=McElhenney=] still kept his day job as a waiter. Eventually, the budget increased with each successive season.
* TheOtherDarrin: An [[http://www.youtube.com/watch?v=6wVdk_PCdgE eighth season promo]] uses this as a gag.
* RomanceOnTheSet:
** Mac & Sweet Dee met through the show and eventually got married in RealLife.
** The Waitress is Charlie's real life wife, which makes the whole RunningGag of Charlie stalking the Waitress some meta-irony.
** Dennis and that pharmacist from "The DENNIS System" are also married, and when the episode is done on stage Rhea Perlman plays Dennis's fake grandmother.
* RealLifeRelative:
** Will Sampson's son played the "Chief" Expy in the OneFlewOverTheCuckoosNest ShoutOut.
** Danny [=DeVito=]'s daughter Lucy has had a couple of one-shot cameos in "Mac bangs Dennis' mom" and "The Gang find a dumpster Baby".
* UnintentionalPeriodPiece: Thanks to the large number of references to the then current events of the TurnOfTheMillennium. The show debuted during that decade, as such many episodes make references and jokes that seem to be ripped from that decade's headlines, such as references to the gas crisis, terrorism, waterboarding, Hurricane Katrina, North Korea, the bar getting a new flatscreen TV and Blu-ray player, just to name a few.
* WhatCouldHaveBeen: The original pilot (without Dee) was called "It's Always Sunny in Los Angeles". It featured Glenn, Rob and Charlie [[AsHimself as struggling actors trying to pitch a TV show]] and MorenaBaccarin as [[TheOtherDarrin Carmen the transsexual]]

!!Miscellaneous fun facts:
* When series creator Rob [=McElhenney=] was asked a question about his character Mac in a featurette, he replied "[[ObfuscatingStupidity I don't know]]... I just show up, say my fuckin' lines, and go home."
* Charlie's play ''The Nightman Cometh'' was for a while actually touring various cities around Philadelphia with all of the original cast members.
* Charlie Day revealed that Charlie's rat-killing speech in "Charlie Kelly: King of the Rats" is basically how he got his role in ''Film/PacificRim''.
* According to Charlie Day, during a recent interview on Conan O'Brien, Danny [=DeVito=] has stated that he's up for pretty much ANY storyline the show might throw at him save for one topic: prison rape. Apparently, [[WagTheDirector [=DeVito=] informed series creator Rob [=McElhenney=]]] that was the ''only'' type of shock plotline that he refuses to have anything to do with.[[note]]Offhand jokes about prison rape are apparently fair game, though. In season six's "Mac's Mom Burns Her House Down", there's a joke about Frank thinking that prison rape happens at nursing homes.[[/note]]
* The writers of ''Series/{{Game of Thrones}}'' were such big fans of the show that they ended up writing "Flowers For Charlie".
* Rob [=McElhenny=] also landed a small role on ''{{LOST}}'' after meeting co-creator Damon Lindelof, who is a big fan of the show.

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