>> The correct business response is to petition management to staff more accordingly so that no table has to be de-prioritized (going by the book on customer service)... Also other measures can be taken, like stocking napkin dispensers and condiments on tables so that trivial requests don't over-burden staff.

Not so sure. Trying to accommodate the worst case customer seems a fools game. You're suggesting escalation, from running the server around to running the management around (and more work overall). Adding napkin dispensers at the tables may go against the entire aesthetic they're looking for, while not doing anything about the ketchup, water, and other frivolous requests.

>> If we create rules like this for how to deal with customers, based on assumptions about them...

There is no choice but to make assumptions about them (even just a generic model of a customer) unless you want to form some kind of relationship with them, which is not really possible in a restaurant setting (with the exception of regulars). Besides, the idea of simply deprioritizing them is quite sound - keep the other customers happy but don't deliberately insult the difficult one. You can not please everyone, so have rules that allow you to please the majority and let the others go.