as a baby i was anorexic, as a teen i compensated my lack of friends by anything sweet. now i am overweight but probably eat more fruit and veggies than many "educated" people of my age (those thinking they know better and giving you advices when eating a pizza
).
as a teen my parents told me i'd look so much cuter with a few less kilos. when you're a teen constantly looking for your parents' approval, that really hurts. since then i don't really care about weight anymore, at least i don't judge people by how much they weigh.
like Andrea said, it's often associated with laziness and eating junk all day. people just don't know what they are talking about. either i ask them how much their foolishness weighs, or i ask them to read the labels of whatever they're eating or whatever snack they have in their bags.