Why are most people so rude and hostile towards fat/overweight people?

I’ve been insulted and called a wide load and fat ass when I was a lot heavier at 252lbs (four years ago) but I’m 6ft. One girl said, “If your fat ass lost some weight, you wouldn’t be knocking EVERY OVER!!!! I don’t respect people that let themselves GO!!!!!” Let’s say I never went into that store with her again. Luckily now I’m 201lbs.