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]

Moby Thesaurus II by Grady Ward, 1.0:

102 Moby Thesaurus words for "gassy":
   aerial, aerodynamic, aerostatic, aery, airy, all jaw, big, bloated,
   blown up, bombastic, candid, chatty, communicative, conversational,
   dilated, distended, dropsical, edematous, effusive, enchymatous,
   ethereal, expansive, extravagant, fat, flatulent, flip, fluent,
   formal, frank, fuming, fumy, fustian, gabby, garrulous, gaseous,
   gasified, gasiform, gaslike, glib, gossipy, grandiloquent,
   gregarious, gushy, high-flown, high-swelling, highfalutin,
   highfaluting, incrassate, inflated, long-winded, loquacious,
   mephitic, miasmal, miasmatic, miasmic, mouthy, multiloquent,
   multiloquious, newsy, overtalkative, oxyacetylene, oxygenous,
   ozonic, plethoric, pneumatic, pompous, pontifical, pretentious,
   prolix, puffed up, puffy, pursy, reeking, reeky, self-important,
   smoking, smoky, smooth, sociable, solemn, steaming, steamy,
   stilted, stuffy, swelled, swollen, talkative, talky, tall,
   tumescent, tumid, turgescent, turgid, vaporing, vaporish,
   vaporlike, vaporous, vapory, ventose, verbose, voluble, windy