Pepe Silvia is a reference to one of the most famous scenes of It's Always Sunny In Philadelphia in which the character Charlie Kelly (portrayed by Charlie Day) goes on a conspiratorial rant about how he believes a person named "Pepe Silvia" does not exist. The scene has gone on to be a favorite in the Always Sunny fandom, as well as finding use as a reaction image on Twitter and an exploitable meme template around the web.
In the episode "Sweet Dee Has a Heart Attack," which first aired on October 30th, 2008, characters Mac and Charlie get jobs in an office building in an attempt to gain on-the-job health insurance. Charlie works in the mail room of the building. Later in the episode, Mac goes to talk to Charlie in the mailroom and discovers Charlie visibly stressed about a supposed conspiracy involving someone named "Pepe Silvia." According to Charlie, he has been receiving mail for a person named "Pepe Silvia," who he believes does not exist (scene shown below).
The scene was an instant hit with Always Sunny fans. A month after it aired, IGN user russianhoodlum posted a thread declaring it one of the best Always Sunny scenes to date. Shortly after the airing, a theory began to spread that Charlie, who is illiterate, was reading "Pennsylvania" as "Pepe Silvia," though that is unconfirmed. The rant grew popular enough that it became the subject of some Always Sunny merchandise in 2016.
The notoriety of the scene made it a popular subject for fan tributes in the form of fan art, animated renderings of the scene, and more. For example, on January 4th, 2010, YouTube user dominiqueDesign posted a Kinetic Typography Animation of the scene that gained over 62,000 views. The video has since been removed.
On March 14th, 2017, YouTube musician David Dockery uploaded a video of himself playing drums along to the Pepe Silvia scene. The video went viral, gaining over 2.8 million views on Facebook, as well as 440,000 views on YouTube.
On Twitter, a screenshot of Charlie during the Pepe Silvia rant has grown as a popular reaction image when joking about conspiracy theories.