Anyone who has ever worked as wait staff in a restaurant or knows someone who has is aware that it's tough work. Working with the general public can be fraught with all types of problems in general, but when it comes to food and drink, people can be picky and exceptionally demanding. Or they could be dim bulbs, which is the case in the article linked below.
Readers submitted stories of especially dense people dining at restaurants, and the replies are varied and, in some cases, pretty pathetic. Here's one example:
"I once had a guy out for dinner with his wife. Although our restaurant is pretty upscale, it is in a touristy area of San Francisco, so we inevitably get the tourists who would never dream of spending that much money at home. This seemed to be the case with these two.
After adjusting the temperature of their water twice, I finally came to take the order. The guy told me he was allergic to all seeds and tree nuts. That’s fine, I pointed out anything on the menu that had pine nuts or seeds so that he knew what would be safe to eat. He then proceeded to order the steak with mustard cream sauce. I tried to explain that mustard is made from seeds—we used real mustard and not the yellow powder stuff. He could not understand, and asked if I could just give him mustard sauce then, without the allergens. When I tried to explain again that the mustard was the part with the allergen, he argued that it was not. Eventually I just offered to adapt the meal to his dietary needs and he agreed. I exchanged the sauce for our housemade steak sauce and brought the meal out. When I returned to check on him, he asked me where the mustard sauce was.
He then proceeded to order the strawberry and mixed nut dessert." -Courtney Martin