The British lottery put out a "scratch-off" game called "Cool Cash". The idea of it is that it's got a target temperature on the card, and to win, you need uncover only temperatures colder than the target. Simple, right?
Since Britain is on the metric system, they measure temperatures in Celsius. So naturally, some of the temperatures end up being below zero. And that's where the trouble came in. So many people didn't know that below zero, larger numbers are lower and thus colder, that the lottery had to withdraw the game!
To quote one of the "victims":
On one of my cards it said I had to find temperatures lower than -8. The numbers I uncovered were -6 and -7 so I thought I had won, and so did the woman in the shop. But when she scanned the card the machine said I hadn't.
I phoned Camelot and they fobbed me off with some story that -6 is higher - not lower - than -8 but I'm not having it.