A person attending a conference or banquet serving deli products in a multiple course buffet who says that they will only have one course of the meal, because of their "diet," but ends up making that one course the equivalent to the amount of courses that everybody else is eating. This word is only applicable when at an event serving DELI foods.
(two men talking to each other at a banquet)
"Dude, do you know how much deli food that chick at my table is eating?"
"Veronica? Yeah, she's a closet dill popper. She says that she will only eat one course because she is on a 'diet', but she makes that one course 3x bigger than everyone else's.