This is a term used to describe a random, out of place, unsightly hair. For example, one long eyebrow hair on an older man, a long dark hair on a woman's chin, or a darker hair growing out of a mole. Any single hair that is obvious and out of place where it is growing.
Etymology: 'Mr. Hair' was originally used by two high school girls in the early to mid-70's in Elgin, IL. The word was then passed down the family tree and eminated to other states in the US like IA and NC.
Dee: Laur, do you um, have hair around your nipples at all?
Laurie: (laughter) No, why?
Dee: Well, I mean, not any?
Laurie: No, why? (exposure of said area) Oh...uh, you have to take care of him. Wow.
Laurie: Go grab some tweezers and let Mr. Hair go on a wild adventure with the trash.