* ActorAllusion: In "Sweet Dee has a Heart Attack", Frank escapes a mental institution in the same manner as Chief Broom in ''OneFlewOverTheCuckoosNest''. Danny De Vito played a minor character in that movie.
* ChannelHop: In an effort to attract interest in [=FX=]'s new comedy-oriented spinoff channel [=FXX=], ''Sunny'' will air its 9th and 10th seasons on the new channel. It's also worthy to note that ''TheLeague'' and ''{{Legit}}'' will also make the hop this fall (''{{Archer}}'' was supposed to go to FXX as well, but, instead, stayed on FX and went from airing on Thursdays to airing on Mondays). [[http://www.tv.com/news/fx-renews-the-league-legit-and-its-always-sunny-in-philadelphia-all-three-shows-will-move-to-its-new-sister-network-fxx-136448148389/ Read more about it here.]]
* TheDanza:
** Charlie Kelly is played by Charlie Day, Mac is played by Rob [=McElhenny=], and recurring character Artemis is played by Artemis Pebdani.
* {{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.
* {{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."
* RomanceOnTheSet:
** Mac & Sweet Dee are married in RealLife, as are Charlie and the Waitress (which makes the whole RunningGag of Charlie stalking the Waitress HilariousInHindsight).
** 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".

!!Miscellaneous fun facts:
* When series creator Rob [=McEllehny=] 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 [=McEllehny=]]] 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 the show, ''Series/{{Game of Thrones}}'' were such big fans of the show that they decided to write an episode for ''It's Always Sunny'' called "Flowers For Charlie" (the 100th episode where Charlie is put under a medical treatment that makes him smarter).
** Rob [=McElhenny=] also landed a small role on ''{{LOST}}'' after meeting co-creator Damon Lindelof, who is a big fan of the show.
* 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]]
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