not give a hoot

from The Collaborative International Dictionary of English v.0.48

Hoot \Hoot\, n.
   1. A derisive cry or shout. --Glanvill.
      [1913 Webster]

   2. The cry of an owl.
      [1913 Webster]

   3. A very funny event, person, or experience; as, watching
      Jack try to catch that greased pig was a hoot.
      [PJC]

   {Hoot owl} (Zool.), the barred owl ({Syrnium nebulosum}). See
      {Barred owl}.

   {not give a hoot} not care at all.
      [1913 Webster]