If someone who has a thin, perfect body and wears a size 3 or less complains about being fat, the rest of us must be planets, amirite?

YESS!!!
It's kind of like an accidental insult.
And then they're always like: "But YOU'RE not fat" , even when they are clearly skinnier than you.

3 or smaller. Really? Thats whats considered skinny, weird O_o