1. Being so fat that your own body fat has the ability of overlapping your eyes causing temporary blindness. Aslo, 2. Being blind to actions that are stereotypically the actions of an obese person.
Ordering a triple burger combo with cheese, super sized, but you want to make sure that the coke is half diet because you're watching your figure. Your Fat Blindness has caused you to overlook the fact that you're stuffing your face like a fat fool.