Why does it seem like "party girls" have perfect bodies?

This is sonething I notice among friends. Girls between the ages of 15-30 who don't look after their bodies at all, binge drink on weekends and take party drugs like ecstasy and MDMA on the regular (not to the junkie extent) seem to have perfect bodies.
Specifically, these girls seem to be stick thin with magically larger boobs. It could be surgery, but I notice this a lot and it's evident in yoinger girls, too.
Wheras I hardly ever see this body shape on fit women. Yes, fit girls look great and have low body fat and some can keep their breasts, but I've never seen a fit girl who looks more socially acceptably "hot" than one of these party girls. These party girls have that typical porn star body type.
What is it? How are these girls staying so thin yet keeping a decent amount of fat on their chests?
Why does it seem like "party girls" have perfect bodies?
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