(US, informal) A self-assertive and arrogant person; a wiseacre or smart aleck.
"It wasn’t until I read Mark Oppenheimer’s charming memoir that I had an apt description of my son: “…a smart aleck is a smart guy gone bad, a boy whose smartness is being used stupidly, while a wisenheimer actually lacks wisdom. He might not be cruel, he might not mean harm, but a wisenheimer is a smart guy you wish had a little less smarts.”