Why do skinny girls call themselves fat?

lol,my friend ,she is skinny but she seems 2 always call herself fat...mayb becuz people around her let her down by calling her that or mayb she has a feeling bout her n her diet ...mayb she eats alot but not get fat..u kno wat i meann btw its usally the people arround who seem to b jealous n make the other person unconfident