The Collaborative International Dictionary of English v.0.48:

Gassy \Gas"sy\, a.
   1. Full of gas; like gas. Hence: [Colloq.] Inflated; full of
      boastful or insincere talk.
      [1913 Webster]

   2. passing intestinal gas excessively; flatulent.
      [PJC]

WordNet (r) 3.0 (2006):

gassy
    adj 1: resembling gas
    2: suffering from excessive gas in the alimentary canal [syn:
       colicky, flatulent, gassy]