1
general::
A day when one's appearance, especially one's hair, does not look attractive. For example, What have I done to upset Martha? Nothing, she's just having a bad hair day. Originating as a humorous statement, this term was soon broadened to mean simply having a bad day, that is, a day when everything seems to go wrong. [Late 1980s] Also see NOT ONE'S DAY.
American Heritage Idioms
2
general::
Phrase(s): a bad hair day
a bad day in general. (As when one’s inability to groom one’s hair in the morning seems to color the events of the day.) • I’m sorry I am so glum. This has been a real bad hair day. • It’s just one bad hair day after another.
McGrawhill's American Idioms And Phrasal Verbs