Thin privilege is when you do not want to share your meal or snack and people accept it and maybe even think it is cute and quirky.
When you are fat and you do not want to share your meal or snack people get upset and think you are gross and selfish.
I just do not like to share my food - it is my food for a reason, because I like it. I do not want anyone else eating my food especially if they are not vegan like me (and therefore have more options than I do) or they think what I am eating is just okay when it is one of my favorites or it was an expensive treat I bought myself or especially if they do not ask and just help themselves to what I am eating. But any reason I have is not okay because I am fat.