1. to assume an air of ...; to act ...; to affect ...; to pose as ...; to behave like ...; to pretend to be ...
after a noun, adjectival noun or adjective stem
そんな風にさ、大人ぶろうとしなくていいよ。You don't have to try to act like an adult like that.
2. to put on airs; to be self-important