I been through the phase of being a fat girl and i totally
understand how it feels like to be discriminated by guys. It sucks
being fat during your teens.
However, whether you want to change it or not also up to you. If
you really REALLY want to diet, die die also you will succeed. If
you half heartedly, then of course you won't succeed.
I used to think think that being nice and all is good enough.
However, life's harsh. 
Even girls go for looks
sometimes. I admit that I also go abit for looks. Who doesn't? Fat
girls are human too. True. I totally agree. But if a fat girl likes
you and you don't like her just cos she's fat, you are jerk.
Do you know that a girl will lose weight for her boyfriend because
she feels that she is loved and she will have more determination to
do so?
But for me, it was cos a guy broke up with me cos i was fat... and
I decided to go on a diet... then go meet him again, make him
regret. WAHAHAHAHAH!
Anyway, yeah... please do not discriminate all fat girls. Some
girls are really nice and with these beautiful traits, they lose
weight and they will become the perfect girl you want.
This is my opinion.
Haha!
