Quote - Well to me, if you can actually SEE someone's hipbones, they're too thin.

The only bone I can accept showing is a collarbone (heh and the skull..) Everything else is ... icky emaciated.

Precisely!  When you start to see bones like the hip, ribs, joints (knobby shoulders, knees, fingers) and outlines of tendons, that's just gross to look at, and is certainly indicative of being under weight.  Percentage of body fat on a women is extremely important for her hormone levels as well as child bearing ability.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi