On the other side of the coin are "Bad Fatties" who eat nothing but bon-bons and baby donuts (thanks to Kate Harding and the other ladies on Shapely Prose http://kateharding.net/), who never, ever exercise or do anything. Of course, their numbers (blood sugar, blood pressure and cholesterol) are NOT good, and they are OBVIOUSLY dying from their DeathFat.
But how can you, the casual observer, tell the two apart?
This isn't City of Heroes/Villians, or WoW or any other MMORPG where people's stats and life bars float above their heads telling you how healthy you are.
Not to mention, IT'S NONE OF YOUR FUCKING BUSINESS!!!! Seriously. It isn't any of your business. Not even a little bit. And I don't care if you HAVE to sit next to them on the bus, or stand near them in a bus shelter, or look at them in public. It remains none of your fucking business. As I've said before, fat people know they're fat, and if shaming people into losing weight worked, we'd all look like Kate Moss. But it doesn't. So knock it the fuck off, asswipe.
Also, just to throw this in the mix there are *gasp* skinny people out there who eat like shit, whose numbers suck, who have diabetes, heart disease and all that crap that is supposed to zero in on the ZOMG FATTIES! And you can't tell by looking at them either.
So, here's an idea. Instead of your default being "Treat fat people like shit because they are OBVIOUSLY killing themselves with their unnatural appetites and willful destruction of the world," why don't you change your default to, "Treat ALL people like human beings regardless of what they look like." That way you don't have to look like an asshole, and I don't have to raise my blood pressure by restraining the urge to slap some sense into that empty melon you have sitting on your shoulders in lieu of a head.