to start being pretentious

Translations
начать вести себя претенциозно
стать претенциозным
начать выпендриваться
начать вычурничать
Definitions
To begin behaving in an affected, showy, or self-important way.
To begin trying to appear more sophisticated, cultured, or important than one really is.
Words
to

preposition
начать
start

verb
начинать
being

verb
быть
pretentious

adjective
претенциозным