Back in college I lost a ton of weight until I was close to, if not actually, anorexic. It didn't matter how often my brother told me I had to eat, or friends said I was too skinny, or that I was way too thin for the blood bank to take my blood. In my mind, I was fat. In the mirror, I saw fat. Other friends who were heavier? "Oh, but they look cute chubby ... I don't."
My mind was incapable of acknowledging reality. Evidence was meaningless. In my own mind I KNEW that everyone else was wrong.
Its very odd to look back at that time, and to see the photos of myself. I try to remember those feelings when I can't fathom a theists inability to hear evidence that contradicts their world view. I was lucky. I seemed to "grow out of" my body disphoria within a year or so. Honestly, I'm not even sure why or how it happened. But that kind of disconnect with reality, if my experience is any indication, is very, very persistent.