* EarWorm: "Come and knock on our door..."
* FanPreferredCouple: Many fans over the years have expressed disappointment that Jack and Janet didn't get together in the end.
* IdiotPlot: See WhatAnIdiot below, and also its tendency to make plots based off stuff from the MistakenForIndex.
* RecycledScript: An early episode had the roommates trying to hide a recently adopted pet from Mr. Roper. Towards the end of the series' run, a similar plot (with a different animal, Mr. Furley and Terri) was used. John Ritter himself later acknowledged the trope said that this was when he realized the series was starting to run out of ideas.
* ReplacementScrappy: Cindy, Chrissy's cousin, was almost a carbon clone with considerably less jiggle factor and the added annoyance of being TheKlutz. Terri managed to avoid this fate by actually having a brain.
* TearJerker: Mr. Furley recounting how he once had a pet as a kid, but it was hit by a car and died, he then decides to name the cat he found after it.
* WhatAnIdiot: This will apply to at least one character OnceAnEpisode.