The Collaborative International Dictionary of English v.0.48:

cock-a-hoop \cock`-a-hoop"\, a.
   Boastful; defiant; exulting. Also used adverbially.

   Syn: boastful, braggart(prenominal), bragging(prenominal),
        braggy, big, crowing, self-aggrandizing, vainglorious.
        [1913 Webster]

WordNet (r) 3.0 (2006):

cock-a-hoop
    adj 1: exhibiting self-importance; "big talk" [syn: boastful,
           braggart(a), bragging(a), braggy, big,
           cock-a-hoop, crowing, self-aggrandizing, self-
           aggrandising]