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1.
Somebody who keeps food in unorthodox locations in hopes of others not discovering their excessive food supply.
Perhaps the most popular Naughty Fatty technique is to hide burgers or other fast food in their vehicle. The Naughty Fatty is given a sense of security by this, knowing there is always a snack in their possession. This can become dangerous if the Naughty Fatty does not practice good hygiene; the smell of rotting food can be mistaken for(or mingle with) body odor, giving the Naughty Fatty the false impression the rotting food is still fresh enough to eat safely. A good way for the Naughty Fatty to stay free of such hazards is to limit the amount of garbage and food waste accumulation in their vehicle to between six and eight metric tons per passenger seat.
by helmetbroom March 08, 2010
 
2.
A naughty fatty is not necessarily FAT, but is a term used to describe a person's eating habits.

A naughty fatty is the kid that hides a few cookies in his pocket for later.
Or eats his entire meal and then the rest of what his buddy didn't finish.

A naught fatty loves treats and might arrive late to class because he stopped on the way to grab a "snack."

He loves snacks.
He also loves buffets.

He'll take a handful of candy from any doctors office or bank dish, as opposed to the general "one per person rule."

A naughty fatty is sly when it comes to food.
He loves eating in all the wrong places at all the wrong times.
Everyone goes to the store for a salad.
Naughty Fatty slips a candy bar on the conveyor belt.
by fpo January 04, 2008