This is just a weird form of bias that is often funny as fuck to call out.
I was dating a girl a few years ago, and hanging out with one of her friends. Her friend was talking shit about a girl and called her a "fat bitch". The girl she was talking about probably weighed 90 pounds soaking wet. My girlfriend was a little thick (nowhere near "fat") and was like "if you think she's fat, what do you think of me?" The girl literally said "you're different". "You mean I'm not a bitch or you don't mind that I'm fat?"
That cunt shut up quick. (I know it's not the same as racial or religious discrimination, but it came to mind.)