The episode: “Gamera vs. Gaos,” ep. 308
The riff: Monologued by Servo as a bunch of excitable Japanese people on the interior of a bullet train bustle around and point at the monster outside.
The explanation: It’s the train setting in particular that inspired this reference to Dial-brand soap. In a series of commercials that apparently aired all the way from the 1950s to 1990s, this exact slogan was used: “Aren’t you glad you use Dial? Don’t you wish everybody did?” The commercials were set in crowded places with lots of people, including on the train.
Novelty factor: Never heard of the slogan before, but I was able to track down the commercial in question.