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.

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.

The kids are really not happy about it, because they have that last name. And so do I, legally!,” his co-starring wife Kaitlin Olson previously joked.