I think it's just something people are sensitive about, and understandably so. Most obese people (by choice; i.e. self admittedly just have a bad diet and sedentary lifestyle) I know are never really offended by memes and consistently express a desire to do better. Fact is fixing the problem is genuinely difficult once you pass a certain point, as it requires a dramatic lifestyle change. Anyone who says that is easy is full of shit.
I avoid jokes like that mostly because it feels like punching down on people who are not happy with their health/weight and struggling to fix it. Especially when it's the typical low hanging fruit, it's just not fun when the joke makes me feel like kind of an ass.
Also it's not like we're unaware of being fat. Like, no, Kevin, I don't need your terrible joke to tell me I'm overweight and should lose some weight. I own a mirror. The "let's make fun of fat people!" crowd always seem to think they're giving us some divine fucking insight.
