I'm posting this as anon, just in case.
At my school, the 'fat' girls are mocked behind their backs. Boys laugh at them, and girls make comments about them when they eat. Even if you're not overweight, you hear things about someone's 'kebab belly' or what she's wearing. Any time someone puts on weight you hear about it. Its not bullying and it isn't even mean, its as if its acceptable to make these comments. I do it, too, because its like I've been trained to.
Nobody makes fun of slim, toned people. I would hate to be mocked behind my back and I like it when people say, 'oh I want your waist' or 'you're so tall and slim'. It feeds the ego, I'm ashamed to say. Because slimness is perceived to be beautiful by the people around me, its what I want to be. Also - you can't buy above a size 14 (sometimes 16) in most of the shops I go to. When a 14/16 is the biggest size it makes that 'large' size unacceptable so you want to be skinnier. The first time I wore a size 8 I was ecstatic and I get a kick from being a 'small'.
To be honest, for me its less about what men think (thought that matters to a degree). Its more about what women think, and how they react because they have the same idea of what is attractive bodywise.