Know-it-all

A know-it-all is a person who pretends to know everything, and attempts to share their knowledge with others at every opportunity. Examples in television include Cliff Claven from Cheers and Brainy Smurf from The Smurfs. Some know-it-alls may possess only a superficial understanding of the subjects which they talk about, while others may in fact know a lot but come across as irritating because of their compulsion to educate everyone they talk to.