fridgeon

A person who can't help checking what there is in the fridge to snack on, often someone else's fridge and always someone else's food or drink. Fridgeons can be identified in a room by the guilty look on their face when confronted by the angry owner of the consumables or their tendency to stop chewing when asked "what are you eating?"

I don't think you can blame the dog this time dear, not unless he's figured out how to use ziplock freezer bags and ring-pull cans - that has all the signs of a teenage "fridgeon".