THIS IS HOW IT ENDS

Once upon a time, there was a girl who was a kind of fat and she had a (almost very) skinny friend.
She was busy with all her plans to lose weight while her friend felt okay with her body.
She worked out in Gym, her friend ate all food she wanted but never got fat.
They liked to hang out together, but she also liked to make fun of her friend.
She said that she's a skinny bitch, she looked unhealthy, had small boobs, and other mean things.
She forgot what she said overnight, but her words carved on her friend's mind forever.

And now her friend's wondering.
Why people say big girls are beautiful but when people say "skinny girls are beautiful" that sounds very obsessed?
Why when people say "You look fatter" it sounds so rude, but when they say "You look skinnier" is okay? Don't they ever think that it could hurt too?
Do people always think skinny people doesn't need pity so we can call them skinny bitches?
Is it okay to make fun of skinny people like that? Or is it just YOU who want to be skinny so bad you start making fun of them just to make you feel okay to be not skinny?