When the narcissistic gang from "It’s Always Sunny in Philadelphia" visited the "Abbott Elementary" school in a crossover episode earlier this year, audiences got to see the two Philly TV universes collide in hilarious ways — all while keeping the episode PG for "Abbott’s" more family-oriented viewers.

In Wednesday's Season 17 premiere episode of "It's Always Sunny in Philadelphia," the "Abbott Elementary" cast gets to cuss — including the "c-word"!

The actors discuss playing best friends and roommates on FX's long-running comedy, which kicks off its 17th season Wednesday, and why "whenever Charlie does something, it titillates Frank."

In an encompassing New York Times feature on the long-running sitcom, the show's creator says he sought to explore the humor in selfish people who are never there for their friends.