quote:

ORIGINAL: Marc2b

WomanlyWiles touched upon it but I think it goes a bit further. That vacant look is one we associate with the (inaccurate) image of the Neanderthal... stooped, knuckle dragging, mouth agape... in short, a primitive. Calling someone a mouth breather is basically calling someone less evolved and therefore inferior when compared to the more evolved (read: socially progressive), enlightened speaker.