Nothing irritates me more than people assuming that because maybe 90% of the population are fat because they eat more than they burn off (and/or eat junk), they can then extrapolate and assume that applies to 100% of the fatties.
Nothing embarasses me more than knowing that pre-babies, in my size 10 ivory tower, I also thought the same.
Having been diagnosed with, variously, ME (an odd diagnosis given I was working a 60 hour week and doing an MSc with two under 3's at home at the time), insomnia, endometriosis, severe hormone deficiency, syndrome X (one for the nutters, that) and so on, I am older, wiser, and fatter.
It was very nice pre-babies to go through a day without craving food, and very nice to not even know the GI load of every single bloody piece of food in Tescos, and nice to go to the yoga and aerobics knowing that my efforts would be actually 'doing good', rather than just holding back the tide. And it was nice to eat carbs too, every now and then, without knowing that I would be asleep within 20 minutes. I've had my DH grab me in a restaurant to stop me falling as I slid off my chair, thanks to a single bread roll. All the problems are slowly starting to fade after 7 years, but it's still an uphill battle. Not helped by having someone ask me 'when I'm due' maybe once a week (something which cannot be corrected without surgery and accounts for an estimated 6kg), or by having a GP simply accuse me of eating doughnuts on the sly when my 600 a day calorie diet had no effect other than to make me very dizzy (I started at a normal diet level of 1400 then dropped by 200calories every 3 weeks in order to test at what point - inter alia - my weight would start to fall)
I am a bit humbler and a shedload less ignorant and judgy than I was before I had kids.