* 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 acknowledge the trope and felt this was when 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.