The Collaborative International Dictionary of English v.0.48:

clowning \clowning\ n.
   1. acting like a clown or buffoon.

   Syn: buffoonery, frivolity, harlequinade, prank.
        [WordNet 1.5]

   2. a comic incident or series of incidents.

   Syn: drollery, comedy, funniness.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

clowning
    n 1: acting like a clown or buffoon [syn: buffoonery,
         clowning, japery, frivolity, harlequinade, prank]
    2: a comic incident or series of incidents [syn: drollery,
       clowning, comedy, funniness]