A
crazy, reckless person. Furthermore, a lighthearted term used to describe a mix between an idiot and a daredevil (either for insult and, sometimes, endearment).
Like the literal black ball used in a game of
pool, an Eight Ball is a living, breathing symbol of both good and bad luck.
Popularized by
U.S. Navy and Marine Corps T.V. shows "McHale's Navy" (1962-1966) and "
Baa Baa Black Sheep" a.k.a. "Black Sheep Squadron" (1976-1978).