The Collaborative International Dictionary of English v.0.48:

Bumptiousness \Bump"tious*ness\, n.
   Conceitedness. [Colloq.]
   [1913 Webster] Bun

WordNet (r) 3.0 (2006):

bumptiousness
    n 1: offensive boldness and assertiveness [syn: bumptiousness,
         cockiness, pushiness, forwardness]