There are shows that come and go, and then there’s It’s Always Sunny in Philadelphia, a sitcom show that somehow never really disappears. It slips under the radar at times, but it always comes back.

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."

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.