This is less dire as your example but I had to explain to some PhDs why rounding each time a number they came across was a bad idea. In that, one should round at the end point of a calculation to limit errors. In fairness, they were only worried about quarterly numbers and wanted them each to be rounded, each time they were calculated. I introduced to them that the raw numbers should be recalculated at the end of the year and not the rounded numbers from each quarter.

That made me look like r/iamverysmart to them but it wasn't until that I brought the error to their accounting department that averaging a bunch of averages was also a bad idea. This is not brilliant stuff in the least but if you live in an industry where basic schooling is lost over time you can look like a genius. As we all know we are talking about just 10,000th place value changes. So nothing dire in the least. But the last revelation netted the company $85,000 in immediate slush. They got a pinball machine. Where did the last years fluff go? I don't know but I'm not about to make anybody else look silly. I'm guessing my hiring manager is gonna get a raise for being insightful.