an obese person with pictures online that make them appear less fat than in real life. secret fatties are known to employ a multitude of techniques. one method to to use their hair to frame their face in a way that makes it seem more slender than would otherwise be the case. secret fatties are also skilled at taking pictures from angles that make their faces seem more angular and attractive, as opposed to the reality, which is a bloated sack of lard.
"she seemed hot online, but when she walked into the bar i knew i was the victim of a secret fatty."