Oh, they did it a few times last season, too. I'd say it's partially because of the move to FXX. They're probably looser with restrictions because it's happened with You're the Worst, too, getting some un-bleeped F-bombs, but honestly, at this point, Always Sunny could've stayed on FX and still gotten away with an uncensored F-bomb. It already happens with Pose, Feud, and American Crime Story.
But one time last season that I remember was on the episode where Mac came out. When he showed the exercise bike, Dee said it looked like he was F******* himself with a *****.