on being nice and frowny at same time

Me: “good grief that starter was awful, so dry and flavourless”
Wife: “I know mine too!”
Waiter: “Everything ok with your meal today?”
Us: “Yes lovely thank you!”

Source: (dead link – https://www.quora.com/What-are-some-examples-of-British-etiquette) What are some examples of British etiquette?