Thin privilege is not seeing your body size specifically being used as a definition for one of the Seven Deadly Sins.

The sin of Gluttony is overconsumption; regular excess of anything, any activity. But it’s only ever defined in images as a fat person, usually surrounded by food. The other sins are represented by actions. Only Gluttony is regularly shown as a fat person. I’ve never even seen a representation of Gluttony that DIDN’T use a fat person who was surrounded by food or constantly in search of something to eat. Popular culture has come to define Gluttony ONLY as a fat person eating; a thin person eating a lot is never seen as gluttonous.