The Collaborative International Dictionary of English v.0.48:

guff \guff\ n.
   1. A ludicrously false statment. [WordNet sense 1]

   Syn: bullshit, bull, Irish bull, horseshit, shit, crap, bunk,
        bunkum, buncombe, rot, hogwash, dogshit.
        [WordNet 1.5]

   2. Insolent or disrespectful talk; as, don't give me any of
      your guff, young lady.
      [PJC]

WordNet (r) 3.0 (2006):

guff
    n 1: unacceptable behavior (especially ludicrously false
         statements) [syn: bunk, bunkum, buncombe, guff,
         rot, hogwash]