The Collaborative International Dictionary of English v.0.48:

Jackanapes \Jack"a*napes\, n. [For Jack o' (= of) apes; prop., a
   man who exhibits apes.] [Written also jackanape.]
   [1913 Webster]
   1. A monkey; an ape. --Shak.
      [1913 Webster]

   2. A coxcomb; an impertinent or conceited fellow.
      [1913 Webster]

            A young upstart jackanapes.           --Arbuthnot.
      [1913 Webster] Jackaroo

WordNet (r) 3.0 (2006):

jackanapes
    n 1: someone who is unimportant but cheeky and presumptuous
         [syn: whippersnapper, jackanapes, lightweight]