Not so much diving but dive boat related.
I was tour leading on a speedboat trip to the Phi Phi Islands in Thailand. I had around 15 customers on-board from all different parts of the world. One female customer (american) asked if she could have a 'coke' out of the cooler box, I reached in and grabbed her a 'pepsi', she asked "don't you have coke" I said "no sorry, we only have pepsi, but that's close enough, right?" - She then went absolutely crazy and demanded a coke, she told us that her agent when she booked the trip had told her that there would be coke on-board.
She sat in the corner of the boat for the rest of the day and didn't speak a word to anybody and refused to even go snorkelling around the beautiful reefs, all because of the coke!
Amazing