crazy as a fox

Adjective

crazy like a fox (not comparable)

1. (simile) Behaving in a foolish, frivolous, or uncomprehending manner as a ruse for concealing clever deeds or deeper intentions.
   • "If old Scraggsy's crazy he's crazy like a fox. What's rilin' him is the knowledge that he's stung to the heart an' can't admit it without at the same time admittin' he'd cooked up a deal to double-cross us. He's just a-bustin' with the thoughts that's accumulatin' inside him."1911, Peter B. Kyne, chapter 18, in Captain Scraggs or, The Green-Pea Pirates