know-it-all
know-it-all {n.}
A person who acts as if he knows all about everything; someone who thinks no one can tell him anything new.
After George was elected as class president, he wouldn't take suggestions from anyone; he became a know-it-all.
- Also used like an adjective.
The other students didn't like George's know-it-all attitude.
Categories:
Source: A Dictionary of American Idioms
