They banned Slaughterhouse Five. Just a little information on Kurt Vonnegut's experience in World War II that eventually inspired him to write the book:
He was sent as a POW to Dresden. On February 13, 1945, British and American bombers destroyed the city by dropping high explosives followed by incendiary bombs. The resulting firestorm turned the non-militarized city into an inferno that killed up to 60,000 civilians. Vonnegut and his fellow POWs survived by accident only because they were housed some 60 feet underground in a former meat locker and slaughterhouse. Vonnegut’s job for weeks after the bombing was to gather up and burn the remains of the dead. His experience at Dresden marked him for life and eventually resulted in his literary masterpiece, Slaughterhouse-Five.
The Florida Department of Education banning one of the most important American novels of all time, that was written by a WWII veteran, from American schools, is the kind of dark humor commentary that you'd find in a Vonnegut book.
I'm taking a swing here but I'm gonna say it's the episode Homer's Barbershop Quartet. I think this is when Chief Wiggum is watching all the talk show hosts make fun of his attempt at a solo career after getting kicked out of The Be Sharps.