Rules rule!

Nor should we expect all particular dietary needs to be catered for everywhere. If we really want dishes free of gluten, salt, MSG, wheat, peanuts, soy, meat, or sulphates, then we must enquire beforehand. As the joke doing the rounds on the internet illustrates, when a customer sees nothing suitable for their diet on the menu, the exasperated waiter suggests that ordering a taxi would be the only suitable option.

Some diners push their special requirements to ridiculous extremes, claiming to be allergic to butter, salt, cinnamon, whatever.... How many people insisted on gluten-free 20 years ago?

The deep-fat fryer is another danger zone. How often is the oil changed? What sort of oil is used? Is the same oil used for fish and meat? Requesting sulphite-free wines when none are listed is just stupidity, of the same kind as those who believe that when they are poured a taste of the wine they have ordered, it is expected they indicate whether they like it or not.

No, stoopid: you are supposed to know what you ordered, and the tasting is merely to ascertain whether that particular bottle is in good condition. In fact, this is a job much better left to the sommelier.