America is the only country to use %m/%d/%y. Since American programmers seem to assume its a good format to use in their scripts (after all, the manpage states: "%D: date"), it would be a good idea if the man/infopage came with a big fat warning like: "%D is considered harmful because for the vast majority of people on the planet, it will be confusing to read for most of the year, but is completely ambiguous for the first 12 days of each month and could be interpreted as %d/%m/%y or %m/%d/%y -- most of the world have traditionally interpreted dates as %d/%m/%y, but most are moving to %Y/%m/%d which is unambiguously understood everywhere. Use something like `date --rfc-3339=date' or +%Y/%m/%d if you wish to uniquely identify a date, which has the bonus of sorting trivially".
(There is a metric buttload of system software out there using date +%D, such as debian's checksecurity, that should never have been encouraged to assume that they could give the user a locale-ised date because of the existence of the nice handy "%D" shortcut; the mere existence of something that claims "%D: date" would lead you to assume it was safe and encouraged to use!) -- Tim Connors