WordNet (r) 3.0 (2006):

schlemiel
    n 1: (Yiddish) a dolt who is a habitual bungler [syn:
         schlemiel, shlemiel]

Moby Thesaurus II by Grady Ward, 1.0:

32 Moby Thesaurus words for "schlemiel":
   asshole, boob, booby, chump, ding-a-ling, dingbat, dingdong, dupe,
   fall guy, galoot, goof, gull, hard-luck guy, hardcase, jerk,
   jerk-off, klutz, loser, mark, mutt, pigeon, poor unfortunate,
   prize sap, sad sack, sap, saphead, sawney, schlimazel, sucker,
   sure loser, unfortunate, victim