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1.
A thin person who exhibits traits that are normally found exclusively in fatties, however due to compulsive exercise or a fast metabolic system is not one him/herself.

Such traits include but are not limited to:

Eating like there's no tomorrow
Sucking dick/pussy better than a Hoover
Fucking for validation
Wearing party hats
Matt eats 6 supersized junk food meals a day, he is such a closet fatty.
by Lewis5D January 31, 2008