I find it funny that the bar soap brand Irish Spring is unknown in Great Britain. The more so that it was sold in West Germany when I was there in 1985; as Irischer Frühling.

Anyway given Pdurrant's comments I'm guessing that it was a big even in an imaginary world, probably some much anticipated episode of a very popular television series? I'd actually hazard a specific guess, but I don't want to be on the hook for the next quiz question. One uses soap in the shower, yes?