"American Dad! - Flush After Reading". In one scene of the episode Roger the Alien (Seth MacFarlane) is dressed as Sherlock Holmes and calls himself Sherlock Groans. He is sitting across the fireplace talking with the real Sherlock Holmes (Tom Hollander).
Roger: "So you got to tell me, what's with the little cape, you're not a superhero."
Holmes: "You're right, why I wear it is the only mystery I could never solve."