It's Always Sunny In Philadelphia: This Theory About The Waitress Will Blow Your Mind

Chicka-dee-dee-dee little birdie, let's dance.

The final point on the matter is the most outrageous but it's also the most genius one of all. In season 5 episode 1, Charlie fancies himself as a bit of a lawyer and reveals that he has an obsession with "bird law".

Whilst the concept of bird law seems entirely made up, it does in fact come in handy in season 11 episode 7, titled McPoyle vs Ponderosa: Trial of the Century, when his outstanding knowledge of birds is used to acquit Bill Ponderosa of any wrong doing.

Not only is he obsessed with "bird law" but there is a running joke throughout the show about just how much he loves birds. He sings songs about eagles, he invents a protein drink made from crows eggs, he designs the gang's wrestling outfits to look like birds, he supports the Philadelphia Eagles football team and, in one episode, even carries around a dead pigeon because he accidentally hugged it to death.

All of this is leading up to one salient point: What is Charlie obsessed with? Birds. What does he frequently call Dee? A. Bird.

So, there you have it, ladies and gentlemen. These subtle (and sometimes not so subtle) clues throughout the show have been a trail of bread crumbs to lead to the conclusion that Charlie's true affections lie with Dee (a waitress) but, out of fear of judgement and disapproval from The Gang, he has forced himself to express them onto somebody eerily similar (The Waitress) instead.