To monkey with

from The Collaborative International Dictionary of English v.0.48

Monkey \Mon"key\, v. t. & i.
   To act or treat as a monkey does; to ape; to act in a
   grotesque or meddlesome manner.
   [1913 Webster]

   {To monkey with}, {To monkey around with}, to handle in a
      meddlesome manner. [Colloq.]
      [1913 Webster +PJC]