I know as a family we sometimes get annoyed. We have a lot of health issues, for example my mum has type 1 diabetes, a genetic disorder, but often can't get finding for things she needs because the departments money is spent on those with type 2 diabetes, usually caused by over eating.
Last year I needed hip surgery by a specialist in teenage hip disorders. I had to wait 6 months in agony on the waiting list for surgery because I was behind people that had weak hips due to over eating (obviously this wasn't everyone in front of me, but one of my doctors once said "wow, finally someone in here that didnt bring this on themselves" )
Is it wrong to walk up to someone you don't know, or someone who's size isn't affecting you and call them fat? Yes of course it is. Even if their weight is affecting you in some wa it is still very rude to comment. I do however understand sometimes why the thought cross people's minds, but no they do not have a right to openly call people fat