Girls say this some times.......!! Boys is this true?

ok!! be honest!!! some girls say that a guy makes fun of a girl or says they don't like her because she's ___fat ex.___!!! is this true? and if it is why do you it? wouldn't it be better for you to say some thing nice or nothing at all? or just say i don't like her? not i hate her or i don't like her because she's fat or ugly? i want to know because i think i may be pretty maybe a LITTLE over weight not fat!!! and i do NOTHING to a guy and when people say "he" likes me. "he" always say NO or ewww or gross!!! why is this? and thanks for your answers!!!