If lots of larger people were being mean or rude to me ALL THE TIME like th epp said I'd question myself and what I was projecting. To say it's because "I'm skinny" and that's it IS VAIN. I'm not trying to be mean here, I'm trying to make people see that what you think is not necessariloy what someone else is thinking!!
They might be rude because they're having a bad day, they might not smile back or be talkatiove if you're not being talkative. I've come across many shop assistants who don't smile or talk and so I don't either. If I'm having a bad day but then someone is really bright and bubbly with me, I can't help but be nice back. It's usually what you project that makes somoene be nicer. But to immediately assume they're not being nice because you're skinny and they're jealous??? Sorry I don't agree with that.
Unless all those people are telling you that's what it is I'm pretty positive that's not the reason.