1
general::
Phrase(s): put on an act
to pretend that one is something other than what one is. • Be yourself, Ann. Stop putting on an act. • You don’t have to put on an act. We accept you the way you are.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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]
American Heritage Idioms