The Collaborative International Dictionary of English v.0.48:

Disreputable \Dis*rep"u*ta*ble\, a.
   Not reputable; of bad repute; not in esteem; dishonorable;
   disgracing the reputation; tending to bring into disesteem;
   as, it is disreputable to associate familiarly with the mean,
   the lewd, and the profane.
   [1913 Webster]

         Why should you think that conduct disreputable in
         priests which you probably consider as laudable in
         yourself?                                --Bp. Watson.

   Syn: Dishonorable; discreditable; low; mean; disgraceful;
        shameful.
        [1913 Webster]

WordNet (r) 3.0 (2006):

disreputable
    adj 1: lacking respectability in character or behavior or
           appearance [ant: reputable]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "disreputable":
   abject, bad, base, bedraggled, beggarly, cheap, contemptible,
   contemptuous, decrepit, derogatory, despicable, dilapidated, dingy,
   dirty, discreditable, disgraceful, dishonorable, disordered,
   down-at-heel, dubious, faded, heinous, ignoble, ignominious,
   infamous, inglorious, iniquitous, low, mean, messy, notorious,
   opprobrious, pitiable, questionable, raddled, reprehensible,
   run-down, scandalous, scruffy, scurvy, seamy, seedy, shabby, shady,
   shameful, shoddy, sloppy, slovenly, sordid, sorry, tattered,
   threadbare, unkempt, unpraiseworthy, unrespectable, unsavory,
   untidy, untrustworthy, vicious, vile, wicked