Sneaky-Fat

An adjective used to describe a person who has the general shape and build of a thin person (as in the face, arms, and legs) but has a pot belly and/or fat ass. Often, these people will wear baggy clothes so that their fat parts are concealed, making them appear thin.

I thought that Tom was a stick, then he leaned back to yawn and I saw his stomach. He's sneaky-fat.