When I walk down the street I see tons of skinny people. I either rightly or erroneously assume that these stick thin people are that way naturally.
I know this is true for some people. They are just gifted with amazing metabolisms that laugh in the face of a challenge like a cupcakes, a hamburgers, or frozen margaritas.
I don't think I ever want someone to see the future, skinny, healthy me walking down the street and think anything other than "Holy crap, she really puts in a lot of thought and work into keeping herself healthy." I don't want anyone to assume that my current, work-in-progress body is a result of me being anything less than diligent.
So, the lesson for me (once again) is that everyone has a back story. I shouldn't resent someone because they're skinny, I shouldn't pity someone who is overweight (though I have tons of empathy/compassion). Who knows, they might be that way because they're unhealthy and deserve of my compassion as well.