It's Always Sunny In Philadelphia: 10 Cameos You (Probably) Missed
6. David Benioff And D.B Weiss
David Benioff And D.B Weiss had a cameo in Season 12, Episode 2, “The Gang Goes to a Water Park.” Here they play life guards at a water park, though they seem to have no interest in their job. This means that they don't interfere with the gang's shenanigans as they run around the park causing mayhem. The two also wrote the episode “Flowers for Charlie” which is Episode 8 in Season 9.
Benioff and Weiss are most known for being the showrunners of Game of Thrones. Due to the mutual love between the creaters of the two shows, Rob McElhenney, who plays Mac, got a cameo in Game of Thrones.