bad hair day
How do you say "bad hair day' in Spanish?
4 Answers
And another...

Andar desgreñado(a) / despeinado(a).

Girls can relate to this due to our long hair. I'm not sure whether there is a real Spanish equivalent for this, because it is one of those idiomatic expressions that is used by one culture and not necessarily by any other.
In California most of us are bi-lingual and carry our idioms quite freely from one language to another. Therefore I will agree with what the SD translator says which is:
"Día de mal pelo (or pelo malo)"

Is a bad hair day just a day when your hair can't be made to look right? Or is it more than that -- a day when many things, including your hair, seem to be out of your control?
"Mal peinado" is sometimes used. It is literally just "bad hairstyle," but in context it might mean more... as with the English.
I have rarely heard it used by a native Spanish speaker. I have never heard "día de mal peinado" or "día de mal cabello" or any other literal translation of "bad hair day."