A while back, the massed ranks of bartending glitterati at the Barbore Speakeasy had a discussion about mistakes made while working. I'd include a direct link, but they've just updated their software and I can't find it. That and I didn't really look for one. You'd have found out the truth sooner or later. Anyway, one poster mentioned that while running a bar at an MTV Awards show in Australia, one of his charges had prepped up a bunch of mojitos with coriander instead of mint. He goes on to explain that a spot of crushed ice and an apple juice float saved the day.
Just to be contrary, I'm not sure I'd class that as a mistake. It's a great save, for sure - it could've gone so very, very wrong but it didn't. Let's put that one under in the pile marked Opportunity - right after Jennings Cox running out of gin. If bartenders didn't make mistakes and create workarounds to overcome them, it wouldn't be nearly as much fun working in bars.