Ear Worm: Deconstructed. When criticized for not having hummable tunes, Sondheim said "if I played it several times, you'd hum it." He did that in here. The most remembered songs are the ones that are played multiple times. "Good Thing Going," for example, is played in the overture, played during "Growing Up," sung at the start of Act II, then sung by itself, then sung again before the transition, then an alternate version in "Opening Doors," which, being heard for the first time, is criticized by the Producer for not being hummable. Also, "Old Friends" and "Not a Day Goes By" are both sung twice in the show.
Not to mention that Sondheim undermines the Producer's criticism by having him hum "Some Enchanted Evening" - and getting it wrong.
Tear Jerker: The whole musical, particularly on the second viewing.