Source : Webster's Revised Unabridged Dictionary (1913)

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

   2. A coxcomb; an impertinent or conceited fellow.

            A young upstart jackanapes.           --Arbuthnot.

Source : WordNet®

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