British & Australian, American & Australian someone who seems to know everything and annoys other people by showing how clever they are.
No one likes him because he's such a know-all.
know-all
1.adjective
conceitedly knowledgeable AUSTRALIA, 1965
2.noun
a person who displays their knowledge in a conceited manner AUSTRALIA, 1934
know-all
A person who acts like they are smarter than everyone else. Primarily heard in UK, Australia. There is nothing more annoying than working with a know-all who constantly tries to outdo everyone else.