I think this is satire speaking of the double-standard in the way that Tumblr users react to fat guy/thin girl pairings compared to the other way around. At least, that's what I'm getting.

OOOOH boy do I have bad things to say about all four of those fuckers. And not just because the fat guy is a neck bearded fadora twat or the the thin one needs to shave the other side of his fucking head, but that the fat girl needs to realize that while genetics DO make some people retain body fat, Genes don't tell our bodies to be borderline obese, and the thin chick, I'm pretty sure, has to be fucked up somewhere in her noggin. Also, who the fuck is commenting in the picture? Do they know they are just drawings? what fucking right do they have to fucking insert themselves in the couple's private business. Also I'd be saying most of that shit about the fat guy myself and I'm a dude.