My WORST experience in a restaurant was in the States, when the customers walked out WITHOUT paying and my supervisor (YES! I was the waiter!) asked me to pay their bill... something that,I learned too late, is illegal!
Needless to say, I did NOT make money (tips) that shift and, I don't recall, but might have been in for a few bucks too!
From then on, I did not use the "book" in which we had to put the bill; I then brought the bill on a small plate, period!
Thinking now about that event, I think the people were "foolish" NOT to spend more since their 4 meals were on me!