Things to say to a fat person:

Stop eating.
You're too fat.
It's not glandular, you've got an eating disorder.
Hey, fatty.
Lose some weight.
Next time you're upset, instead of reaching for the chocolate, reach for the noose.
Look, there's a fat guy.
Holy shit, that's some fat guy.
Is it a bird? is it a plane? No it's some fat guy.