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to assume an air of ...; to act ...; to affect ...; to pose as ...; to behave like ...; to pretend to be ...
to put on airs; to be self-important
彼はいつも偉ぶって話すから嫌だ。
I don't like how he always talks in a superior manner.
知ったかぶるのはやめたほうがいい。
You should stop pretending to know everything.
大人ぶる子どもの姿がおかしかった。
The child acting like an adult was funny.