That's the 'kin point really.
In everyday life a roll of the eyes could be meant totally sarcastically and very aggressively - or - at the other extreme could be meant jokingly in humour. The facial expressions that precede it and follow it reveal its actual intent. But in text alone there is simply too much ambiguity. That's why you would never find in a novel, for example, a simple description that X rolled his eyes. It would always be qualified along the lines of, X rolled his eyes in disgust, or X rolled his eyes jokingly, a grin slowly spreading across his face.
I guess what I'm saying is that unlike the smilies for Mad, Embarrassed or Confused, which have relatively clear cut meanings in most cases, the Roll of the Eyes or the Big Grin can often be close to meaningless without qualification.