seem very self-satisified like you have just had some kind of success He looked like the cat that ate the canary when he came in with a smile on his face.
LOOK LIKE THE CAT THAT ATE (SWALLOWED) THE CANARY
Meaning of LOOK LIKE THE CAT THAT ATE (SWALLOWED) THE CANARY in English
English idioms vocab. Словарь английских идиом и выражений. 2012