1.79. Hans and Fritz are German spies during World War II. They try to enter America, posing as returning tourists. Hans is immediately arrested. (JM, originally from How Come -- Again?)
1.79 answer: Hans and Fritz do everything right up until they're filling out a personal-information form and have to write down their birthdays. Fritz' birthday is, say, July 7, so he writes down 7/7/15. Hans, however, was born on, say, June 20, so he writes down 20/6/18 instead of what an American would write, 6/20/18. Note that this is only a problem because they claim to be returning Americans; there are lots of other nations which use the same date ordering.