tipping? do you or don't you?

[Olaf]

We also tip the expected 15%-20% in the USA - sometimes more if we have shared a meal. On a couple of occasions over the years though, we have noticed that a gratuity has been added to our bill in the US automatically and on further investigation, it turned out it was because we were British!

If I were you, I'd have circled it, and written in a "thanks, I was planning on leaving 20%".