Being skinny yet totally out of shape is more common then people think. My sister has always been very thin yet never works out and eats nothing but junk; her favorite snack as a kid was bacon dipped in mayonnaise. Right now she is 5'9" and weighs about 110 lbs, wears a size 0 and never works out, ever. She is the textbook example of what "skinny fat" is.
On the other hand, I've always struggled with my weight, yet I am an avid runner and have a very healthy diet. I'm 5'7", 160 lbs and wear about a size 8, however my body fat percentage is 16% (great for a female) and I am visibly muscular. What is ridiculous is thst people think I'm fat and my sister is skinny, therefore I'm not as in shape as her... we need to educate people about what being "fit" really means.