A word often used by anime characters. (Usually the anti-social/ broody/ cold/ tortured types. Ex. Hiei from Yu Yu Hakusho.)
It is a universal bitchy answer to anything anyone says. The character says it when they could care less, or when they are being a
jerk. Which is probably all the time. (Can even be used as a greeting, it's
pretty versatile.
Like grunting to communicate.)