When a fat person brainwashes themselves into thinking they're beautiful, it's generally accompanied by a scornful dislike towards normal beauty standards. They think "no, I'm not fat. Everybody else is just too skinny!" and then apply that logic to other deformities, like actual midgets or people who were in horrifying accidents.
This leads to a warped sense of what's considered "beautiful" by them. To them, ugly becomes breathtaking and "normal" becomes an attack aimed directly at them.
