Feigned madness

"Feigned madness" is a phrase used in popular culture to describe the assumption of a mental disorder for the purposes of evasion, deceit or the diversion of suspicion. In some cases, feigned madness may be a strategy—in the case of court jesters, an institutionalised one—by which a person acquires a privilege to violate taboos on speaking unpleasant, socially unacceptable, or dangerous truths.
Modern examples.
To examine the system from the inside.
Investigative journalists and psychologists have feigned madness to study psychiatric hospitals from within: