xkcd #3232: Countdown Standard
Title text:
Anyone who is caught counting 'three ... two ... one ... zero ... GO!' will be punished with a lifetime of eating only ISO standard food samples.
Transcript:
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Source: https://xkcd.com/3232/
Certainly agree that I've never asked or been asked about this before!
My original thing, though, was that it couldn't be used interchangeably for fractions or percentages, but could for whole numbers. So your example with 50% clearly doesn't work, but 3 times more and 3 times as much could more easily mean the same thing.