What is your best comeback line for when someone calls you fat?

Have you ever lived your life putting yourself in other people's shoes, and know why they eat a lot and get fat easily? Don't judge us for being fat, because when we sleep we do dream seeing ourselves with a sexy body, and the only way for us to make it come true is by going through operations, like cutting our gastric stomach inside and live with scars in our bodies.
Instead of judging, help them embrace their body and motivate them to lose weight in a way they don't get bored of going through failed diets.