A bad hair day is also a day when everything is going bad. It has nothing to do with how one's hair really is, it's just that everything is going wrong. The term "bad hair day" derives from how psycho one feels because everything is going all wrong on a particular day!!
Grabs handsful of hair and tugs in indesperation, "Arrrrrgh!! I'm having such a bad hair day!!"
The act where in the male receives fellatio by a female wearing a baseball hat and at the point of no return, releases himself into said baseball hat, then putting it back on her head and twisting it around Jorge Posada style.
Shes been in the shower for an hour cause he gave her the ol bad hair day.