The expensive rome ice cream (not so expensive)

Rome, Summer 2014. The news by reports an american couple with a friend was charged €42 for three ice creams and a water bottle behind Trevi Fountain. They had a discussion with the owner assuming they paid €59 for a full lunch including a wine bottle. They came back the next day with two police men, the owner showed off the clear price list: ice cream in glass cup is €13 w/ service table. I still wonder why some people want to show a good impression to their friends while sitting on a bar table and not checking the menu and then showing off completely the opposite bad impression start complaining for the prices.