Should Beauty be no less similar to character/physical traits such as determination or the length of my nose - i.e. Beauty as a statement rather than compliment - then 'thank you' is not in order. It is clear, however, from the context that it was meant to be some kind of pat on the back, i.e. 'well done you're beautiful/not half bad-looking/of tolerable physical appearance', which means that I, probably out of reflex (though it's a poor excuse), did after all say 'thank you'.
In truth, my ego is sufficiently inflated without adding to it false commendation (for it is surely false when we attribute merit to qualities that should be by nature impartial and, arguably, irrelevant). But I do feel flattered. Which probably suggests some hegemonic conditioning or inundation of mass culture 'consent', but flattered is honestly the last thing I wish to be. What I wish to do instead is defend women, all women, all men too, because there should be no need to be beautiful to be interesting.
Image credited to: http://ww1.prweb.com/prfiles/2007/02/08/503752/image1.jpg