A euphemism for wiseass, smartass, cracking wise.

Frank Sinatra was prone to use this on stage at The Sands during the Summit Meeting the Rat Pack had there in 1961. When he did, he was usually referring to Sammy Davis, Jr..

Frank: Sammy, what the... why aren't you wearing your nice dinner jacket like the rest of us?

Sammy: Well gee Frank! You know what happens when I wear all black!

Frank: Don't be a wiseacre!

wiseacre

A foolish conceited fellow.

The 1811 Dictionary of the Vulgar Tongue.

Wise"a*cre (?), n. [OD. wijssegger or G. weissager a foreteller, prophet, from weissagen to foretell, to prophesy, OHG. wissagn, corrupted (as if compounded of the words for wise and say) fr. wizzagn, fr. wizzag a prophet, akin to AS. witiga, witga, from the root of E. wit. See Wit, v.]

1.

A learned or wise man.

Pythagoras learned much . . . becoming a mighty wiseacre. Leland.

2.

One who makes undue pretensions to wisdom; a would-be-wise person; hence, in contempt, a simpleton; a dunce.

© Webster 1913.