nobody's fool

plural nobody's fools

1. set phraseA person who is not easily deceived or victimized; one who is perceptive, clever, or thoroughly common-sensical.

   You didn't like school / And you know you're nobody's fool / So welcome to the machine

   1975, Roger Waters, “Welcome to the Machine”, in Wish You Were Here, performed by Pink Floyd

   4 more examples

   Also, he is nobody's fool. He possesses the brain and strength of character to play his part.

   1910, Jack London, Theft: A Play In Four Acts, Characters

   He was nobody's fool, and there was no doubt but he had very soon detected the trick his cousin had played upon him.

   1914, William MacLeod Raine, chapter 6, in The Pirate of Panama

   But one could tell from her assurance that she was nobody's fool and would stand for no nonsense.

   1986 January 18, Jack Anderson, “Dance: A Tribute to Jerome Robbins”, in New York Times, retrieved 12 May 2015

   Yet her musical stature, and intelligence are undisputed: she is nobody's fool, and she remains, quite simply, a perfectionist.

   2003 December 22, Roderic Dunnett, “Cecilia Bartoli: The singing pioneer”, in Independent, UK, retrieved 12 May 2015