S13E05 The Blunder Years
The Simpsons go to see stage hypnotist Mesmerino, who regresses Homer to his early teens when he and his friends discovered a rotting corpse in an old quarry. The police investigate and find the corpse's skeleton is still there. Mr. Burns explains that it is the corpse of the father of his adoring assistant Smithers,who died saving the town from a nuclear meltdown. Whilst Smithers is pleased to learn that his father died heroically Homer takes the skull home as a souvenir.