The Collaborative International Dictionary of English v.0.48:

Bumptious \Bump"tious\, a.
   Self-conceited; forward; pushing. [Colloq.] --Halliwell.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bumptious
    adj 1: offensively self-assertive [syn: bumptious, self-
           assertive]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "bumptious":
   aggressively self-confident, arrogant, audacious, biggety, brassy,
   brazen, challenging, cheeky, chesty, cocky, cold, conceited,
   contemptuous, contumelious, cool, daring, defiant, defying,
   derisive, disdainful, disregardful, familiar, forward,
   greatly daring, hubristic, immodest, impertinent, impudent,
   insolent, insulting, know-it-all, obtrusive, overpresumptuous,
   overweening, overwise, peacockish, peacocky, perk, perky, pert,
   presuming, presumptuous, procacious, puffed up, pushy,
   regardless of consequences, saucy, self-conceited,
   self-opinionated, smart-alecky, stuck-up, swelled-headed, uppish,
   uppity