Monobrow.com is a website that celebrates "the unity of eyebrows." It thinks that people with one eyebrow (isn't that used to be called unibrow?) are cool ;)
My favorite is their Mono Bro of the Week: This one is New York cabbie Azize Hasad whose symmetry of eyebrow and moustache is downright genius.
Link - via Miss Cellania
Maybe it's just no one wants to tell that person they have a unibrow and it looks funny.
UNI comes from "unus" (Latin for "one")
MONO comes from "monos" (Greek for "one")
They used to teach things like this in school.