The Collaborative International Dictionary of English v.0.48:

Ungentlemanly \Ungentlemanly\
   See gentlemanly.

WordNet (r) 3.0 (2006):

ungentlemanly
    adj 1: not befitting a gentleman [syn: ungentlemanly,
           ungentlemanlike]

Moby Thesaurus II by Grady Ward, 1.0:

19 Moby Thesaurus words for "ungentlemanly":
   boorish, caddish, coarse, crude, ill-bred, inconsiderate,
   insensitive, loutish, louty, nasty, offensive, tactless,
   unfeminine, ungenteel, ungentle, unladylike, unrefined,
   unsolicitous, vulgar