A Black Sheep is somone who doesn't follow mainstream days, Somone who doesn't care what is in or out. Usually somone causing some Mischief, or terror and laughing about it. Somone that stands out in the crowd.
A Black Sheep can also be a backstabber.
Alex "Dude Mary Roach is such a Black Sheep... He told my girlfriend I was cheating on her"
Members of the toughest, flyingist, darn Marine Corps squadron in the Pacific Theater of World War II. Originally wanting to be called "Boyington's Bastards," but "Black Sheep" was a bit more printable.
The Black Sheep Squadron TV show is not a very accurate portrayal of the real day-to-day life of the sqadron.