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.
Naughty Fatty slips a candy bar on the conveyor belt.