I get where you are coming from OP. I am also called a skinny bitch by my friends (one of which is obese).
I don't know why people think it is acceptable to comment on people being 'skinny' (HATE that term) but not acceptable to comment on being fat.
I have always been thin. Teased at school for it, people thought I was anorexic. Having kids stopped that for a while but now my body has gone back to being thin again and I can't gain anything, despite me eating loads of crap.
I am thin but have curves as well, I thought I was finally happy with my figure, and had left the negativity of school behind, until a recent conversation with a friend (the obese one).
Me and 2 friends talking, obese friend talking about how she wants to lose weight and saying that she wants a figure like our friend. I said what's wrong with mine, in a jokey way, and she just said "oh no, your too skinny". Conversation carries on and my friend who has the figure that obese friend wants wears the same size clothes as me. Not sure what the difference is. 
Now I am back to being paranoid about being too thin (I am a size 10 with a waist, 34D boobs and a bum that does stick out slightly although I do wish a bit more) whereas before I was quite happy with my figure.