Sorry, disagree; the LEO translation looks fine to me.
The (ironic) point is that even when only relatively minor things go wrong -- as when women/girls have a bad hair day in the literal sense -- it can totally ruin the whole day in the figurative sense, putting you in a lousy mood and making you grumpy and no fun to be around.
BAD HAIR DAY -- n. (1991) a day on which one's hair is particularly unmanageable; hence, a day on which everything seems to go wrong. Colloquial, originally US. 1994 Post (Denver): Soon you will notice how much less complaining you do, even on bad hair days. From "20th Century Words: The Story of New Words in English Over the Last 100 Years" by John Ayto (Oxford University Press, New York, 1999).http://phrases.shu.ac.uk/bulletin_board/12/me...
bad hair day - Noun. 1. A day when one is unable to arrange one's hair into a satisfactory and pleasing style.
2. Used figuratively for a problematic and difficult day.http://www.peevish.co.uk/slang/b.htm
The expression "bad hair day" is usually used in informal contexts to mean "a bad day in general".http://www.hindu.com/edu/2003/12/08/stories/2...
bad hair day
noun 1. a day in which one cannot get one's hair to look good. 2. a day in which one is in a bad mood and nothing goes right: Having a bad hair day, are we?
Aussie Slang Dictionaryhttp://modernisms.tripod.com/group/id15.html
Several references also cite Buffy the Vampire Slayer, starting with the 1992 film, which would suggest California 'valley girl' slang.