To behave misleadingly, esp pretentiously; SHOOT someone A LINE (1934+)
Idioms and Phrases with put on an act
put on an act
Pretend, especially in order to deceive; also, show off. For example, We were afraid Charlie had hurt himself, but he was just putting on an act, or We know you're a good swimmer—stop putting on an act. [ c. 1930 ]