pretending or claiming to know much about almost everything
a know-it-all person
One who acts as if he or she knows everything, as by offering unsolicited advice or rejecting others' suggestions.
- (pejorative) Someone who obnoxiously claims to be knowledgeable on a subject.
- We had it all figured out, but this know-it-all marched in with "the correct way of solving it", leaving our experiment in shambles.