dianavan, I am a bit concerned about two items:
If one accepts that the girl was rude, and I certainly do, then responding in a similarly rude way does not, to me, indicate that one is 'wiser and deserving of respect.' To me it seems that, no matter the provocation, one has sunk to the level of the rude girl.
And I am concerned that one day someone will ask some young person 'Are you handicapped?' in a forceful way, and the appropriate answer will be 'yes' due to something not immediately obvious, and both parties will be embarrassed.
Much as I deplore some behaviors, including taking the 'saved' seats without need, and the extreme rudeness of the girl in the original post, it does not seem likely that anyone's manners will actually be improved by such responses; they seem to me to add to the total unpleasantness in the world. I suspect sudden temporary deafness is more useful. I do admire an answer that is neutral and amusing but not rude, such as "I don't know, the label's fallen off," but many of us are not able to come up with that sort of response on short notice.