act like a know-it-all

Translations
faire le je-sais-tout
Definitions
To behave in a manner that suggests one has extensive knowledge or expertise on a wide range of topics, often to the point of being arrogant or dismissive of others' opinions.
Words
act

verb
agir
like

preposition
comme
a

article or possessive pronoun
un
know

verb
savoir
it

pronoun
le
all

adjective
tout