Nancy Know-it-all 

A person who behaves as if they know everything, specifically in the context of a social atmosphere in attempts to look cool around others.

Jack: I got some champagne for the party!
Derek: Actually Jack, champagne is from one specific region in California, you just technically brought sparkling wine.
Jack: You're being a little Nancy Know-it-all Derek...

Nancy Know-it-all by MagicManMatt October 30, 2017