This is usually exclaimed at volume and in a dubious Scottish accent, in an attempt to copy the style of the actor in the film 300. Because the accent has a tendency to slip into Northern Irish, Mark's impression has been noted to sound more like that of the late Reverend Ian Paisley. This led to the additional phrase, Sparta Says No.
Incidentally, Butler's appearance in the film Gamer led to the phrase Woola Woola Woola.
See also Shut up Buttwad.