It's Always Sunny In Philadelphia: 10 Best Recurring Jokes
1. Dee's A Bird
Dee is a hilarious character, but she is also a somewhat talented person and a decent friend on occasion. Still, above all else - Dee is a great big flightless bird.
Calling Dee a bird is such a strange gag, as it's never made any sense yet never fails to capture a laugh. The joke originated in the episode "The Gang Gives Back" when Mac mocked Dee for wearing a yellow jumpsuit, comparing her to Big Bird. From there, the joke evolved and turned into something that constantly gives Dee grief.
She is always getting insults hurled at her, and this is one that's tossed around a lot, with her barely being able to go a few episodes without being compared to a bird.
The best implementation of the running gag had to be in "Who Got Dee Pregnant?", where each time the gang remembered the drunken Halloween night, they pictured her becoming more and more like a bird until she just ended up being an ostrich.
Of course, Bird isn't the only word beginning with a b that they constantly call her, but the other one's best left to your imagination.