It's when they stop at the convinence store to buy some Fluffy Whip, and Dewey gives the clerk the credit card. The clerk doesn't swipe the card, because Doug grabs it and calls "The credit card vixen". He asks her, "Guess where I went tonight", and she answers, "The one stop market on Ventura". But she couldn't have known that, because she never got a credit card number, and the clerk did not swipe the card. She also said the card was good, but did he swipe the card...no!