Fat Pride

Thighs, originally uploaded by camille94019.

I don't know why this pictures makes me so happy. If you look carefully, you can see where the sand chaffed her inner thigh. I was showing it to H in the staff room at work, and I announced that I was "obsessed with fat people!" One of our thin coworkers, who was also there, started violently when I said that. She looked at me pointedly.
"Have you ever been fat?" I asked her.
"No."
"I have, and its a sensitive topic"
At this point, H laughed nervously, and we dropped the topic.

Why does fat make people uncomfortable? It truly is a sign of being american and affluent (at least from a global perspective). What is wrong with that?