Know-it-all (noun)

  1. A person who acts as if they know everything and refuses to accept advice or information from others.
  2. A person who is irritatingly confident in their own knowledge or expertise.

Origin:

Compound of know + it + all.

Examples:

  1. He's such a know-it-all, he won't even listen to other people's opinions.
  2. The know-it-all attitude of the new employee was off-putting to her colleagues.
Some random words: guru, besiege, counteroffer