"Grampa vs. Sexual Inadequacy"
Season 6, Episode 10

Normally, you wouldn't want to buy a miracle libido enhancer from a raving old man, but put that old man in a crispy white suit and all of a sudden you're reaching for your wallet. While selling Simpson and Son’s Revitalizing Tonic, Grampa suits up in his finest garb and instantly sells out every batch he and Homer mix up in the bathtub.