Flat Fat
When someone has a flat stomach only made up of fat.
Person1: Dude look I have a sexy flat stomach
Person2: Naa dude, that's just flat fat
Person2: Naa dude, that's just flat fat
Flat Fat
When a really obese people loses a ton of weight in a short amount of time, making their appearance seem pinched or unnaturally small
Damn dude, John's wife lost 300 lbs in a week! What a flat fat!