I think the writer is trying to be snarky and funny or something, but he or she comes off as dismissive and mean instead. I think the point is that we should tell people how fat they are, instead of being nice about it. Because that surely will help people lose weight. Because society right now is too nice to fat people. Oh yeah, that's the problem.
Fat's a delicate subject. We don't have fat sizes; we have "women's" and "big and tall," and then something called "plus size," which at least one youngster once misheard as "bus size." Jeans are not made "tent-size" for overeaters, they're just "roomier," as if room-size pants weren't large.