Fetching details from the dictionary...

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
彼はいつも金持ち振っている。
He always acts like he's rich.
彼は専門家振って難しい話をしていたよ。
He was talking as if he were an expert.
知らないのに知ったか振りはやめなさいね。
Stop pretending you know everything.