Meme History: Pepe Silvia 

The driving force behind It's Always Sunny in Philadelphia’s ”Sweet Dee Has a Heart Attack,” is that Mac and Charlie need a job—any job—in order to get health insurance. To that end, they end up in an office mail room, where Charlie becomes obsessed with someone called “Pepe Silvia” who he believes doesn’t exist.

https://www.youtube.com/watch?v=VOfJzeJIuDo&ab_channel=TheDailyDot

It's Charlie’s third scene in the office. The first features him acting fairly normally, joking around with his new coworkers.