You shouldn't be telling a girl she's too fat just like you shouldn't tell a girl she's too skinny. Everyone has their own unique body shape and the way that their body is filled out. Yes some people may be graced with naturally skinny nature and some may be graced with bigger boobs or butt.
In high school I used to get told all the time that I looked too skinny, or that I looked like I needed to eat more. People often told me to "Eat two burgers because you could use some meat on your bones." It never feels great to have someone comment on the way your body looks, sometimes even if it is positive. I hide the fact that I only ate one meal a day, if that, and ran three or more miles religiously on the treadmill every night.
I played for a club volleyball team so everyone just suspected that my skinny, semi muscular body came from all the athletic activities I spent my days doing. No one ever thought a second about me not eating properly. People would comment on how I had mosquito bites for boobs and my butt was as flat as a board. I actually had someone doing an art project on eating disorders ask to use my silhouette because I was "freakishly skinny".
There is no real thought behind the comments people make towards other people. Having an eating disorder is a real mental illness and the way it makes you feel is just awful. You look at your body like it will never be good enough even if you are as skinny as ever. Personally the thought of gaining any weight was disgusting. I would feel uncomfortable with my body if I ate two or even three meals a day. If I felt as though I was gaining weight in a certain area I would not eat for a while.
Despite the negative comments, you also get the positive comments. "You are so skinny and fit I'm jealous" or the guys that swoon after you because you are on the skinnier side and maybe you have "skinny abs". This only adds fuel to the fire because then in some twisted way you begin to think that people like you better that way and maybe more people would like you the skinnier you get.
But I am here to say that you can beat it and you can rise from the dark depths of an eating disorder. It starts with working on yourself and not worrying what other people have to say. It goes in baby steps whether its graduating from eating just one meal a day to eating a meal and a snack. The mental toll that having an eating disorder takes on someone is strenuous. You never truly know what battles people are fighting on the inside and that's why I believe no one should comment on the way anyone's body looks.
People need to stop fat shaming and skinny shaming everyone they see.