2. 'The Nightman Cometh' (Season 4, Episode 13)
If a minor character, joke, or bit of backstory works, IASIP's writers will bring it back and build it out; this is a show that wastes absolutely nothing. Charlie's tossed-off song about "the Nightman" and "the Dayman" from the "Sweet Dee's Dating a Retarded Person" episode is expanded into a full-on stage musical, with the gang helping to mount a twisted little fairy tale about a boy who keeps getting molested by supernatural creatures. The comedy is in the production's rehearsals, where folks keep missing their marks, botching their lines, and annoy their director by pointing out how much rape is in his play. It's both a crackerjack bit of backstage farce and a peek into the psyche of the show's saddest, loopiest character.