If you are going to run a cafe/restaurant/tea room etc then you will have to deal with the public.
Fact: People do odd things, ask for odd things and say odd things.
If you don't want to deal with the public, then don't run a cafe.
If you are a cafe owner, unless you have a minimum charge per person, you have to accept that some people will spend lots of money and other groups very little. Without a minimum charge, there really is no way of preventing this.
As a business owner, I'd save my outrage and refusal of customer requests for those that no doubt will come, which are genuinely odd and unreasonable.....asking for an extra cup is not one of those kind of requests. Owner should just smile and give them the cup.
And for all those business owners on here are would like to see all the tight arse customers bugger off, and who get so furious about customers asking for things like the heating on (the absolute cheek of it) I wonder if it is time to leave the hospitality business. Sure, business life is tough and turning a profit might not always be easy, but when you start to see the customer who sits a bit too long at the cafe table, or who wants extra milk, or an extra cup as the enemy, then it really sounds like there has been a lack of perspective.