As Full as a Boiled Owl
There’s a thin line between being perceived as confident and cool and being seen as being full of yourself. Nobody likes people that seem conceited and self-centered – it’s really annoying. But the idiom itself is pretty funny. I mean, isn’t everything that isn’t hollow full of itself? What else would it be full of?

This reminds me of those weird dishes in which they fill food with a different version of the same food, like meat-filled meat for instance. There are veal chops with chorizo stuffing and roast turkey with pepperoni stuffing. There are also those jacket
potatoes which are filled with mashed potatoes. I can just hear someone saying: Isn’t that potato full of himself??