Source : Webster's Revised Unabridged Dictionary (1913)

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

Source : WordNet®

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