a wise guy

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
See also: guy, wise
References in classic literature ?
Makin' free to spit out what's in me," Matt said one day, "I beg to state that you was a wise guy all right when you paid the price you did for that dog.