doofus

from WordNet (r) 3.0 (2006)

doofus
    n 1: a stupid incompetent person [syn: {dimwit}, {nitwit},
         {half-wit}, {doofus}]

from The Collaborative International Dictionary of English v.0.48

doofus \doo"fus\, n.
   a person who is stupid or inept; -- used contemptuously.
   [Also spelled {dufus}.] [Slang]

   Syn: dingdong, ding-a-ling. [PJC]