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.

Some of their antics ranged from Dennis creating his own fully functional coffee shop made entirely out of the school’s science equipment to Frank peeing in a kid’s locker, and all of them cutting th...