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I work in a grocery store meat department, and part of my job is breaking down the newly-delivered pallets in the morning.
Ground beef was on sale and the warehouse had allocated (i.e., sent us extra on top of what we ordered) way too much. Each box has a production date and a use by date, but the text is very small, so I am supposed to write the day of expiration (excluding the month, since ground beef gets only 20 days on the shelf anyways; so a box that expires July 5th would get "5") in larger size and circle it.
I was very sleep deprived and on some of the boxes accidentally wrote the day of the production date (last month) instead of the expiration date, making it seem like they had 10 extra days. So the butchers ground other boxes before those ones, and the mistake was only discovered two days after the last two remaining (roughly 80-lb.) boxes had expired.
A funny mistake that's not mine is when a new hire, on his second day, was told to run our cart of fresh pickles. When he pushed it over the threshold from the backroom to the sales floor, the too-large, precariously-stacked cart completely collapsed, causing dozens of jars of pickles to smash (and to be clear, I did tell him how to push carts backwards over the threshold so that exact thing doesn't happen - he just didn't do it).
And to top it off, he wasn't wearing his slip-proof shoes (even though he had been told to multiple times), so when he was carrying a box of sauerkraut to the department to be written off, he slipped in the pickle juice on the floor and dumped sauerkraut all over himself.