How much skin can be stretched?

When a fat girl eats a cheeseburger, people think, "Ew, eat a salad."

When a fat girl eats a salad, people think, "Is she trying to lose weight or something?"

..but when a SKINNY girl eats a cheeseburger, people think, "Wow, she eats and eats and never gains a pound."

and when a SKINNY girl eats a salad, people think, "Why is she eating a salad? She doesn't need to lose weight."