Many years ago a friend who hadn't been out of the U.S. since his stint in Vietnam asked if he could join me on a trip I was taking to Latin America. I figured there was no harm so I told him he was welcome to come along. As luck would have it, we had to change the date of our return flights. The agent at the checkin desk for the return flight changed our tickets and as we were just about to walk away from the desk, my friend asked the American Airlines agent (who was already mid way into handing us our boarding passes) "but you forgot the change fee".

Thank goodness he was of high moral character as I'd have strangled him otherwise.