a wise guy

(American & Australian informal) also a wise-ass (American very informal!)

someone who is always trying to seem more clever than everyone else in a way that is annoying Okay, wise guy, if you're so damned smart, you can tell everyone how it's done! He's just some wise-ass who thinks he knows all the answers. (American & Australian informal)

See an old head on young shoulders

Common Names:

Name	Pronounced	Usage
Annabelle	AN-ə-bel (English)	English, French
Marcus	['ma:kəs]
Emilija	EM-ee-lee-yah (Serbian, Croatian)	Lithuanian, Slovene, Serbian, Croatian, Macedonian
Carla	['ka:lə]
Carrie	KER-ee, KAR-ee	English
Kathie	KATH-ee	English