Yeah Just imagine shapeless, denim, relaxed to the point of slobbish sack-like WW2-esque casual wear was aimed at thin people, there would be outrage!
For how much they go on about fashion FAs know absolutely nothing about it. I am not a fashionable man but I have the benefit of having eyes and denim relaxed wear (dungarees, oversized 'mens' shirts etc.) has been in style for the last 2 or so years.