It is someone that always looks dead skinny yet seems to eat what they want and do very little exercise. It is presumably genetic.. their body is small in mass but they have a high fat, low muscle ratio.
Callum Best is skinnyfat. Reportedly, although quite skinny, he has 22% body fat.
After a long workout at the gym, John caught a case of skinnyfat and proceeded to eat a large meatlovers pizza from Pizza Hut by himself.
"She ate a double-quarter pounder meal from McDonalds, 3 pieces of chicken from KFC, and some yogurt from TCBY....all in one sitting"
"Damn she THICKE, SKINNYFAT!!!!"