Ron,
    The "mutt`s nuts" suggests the subject is regardrd as being   
    one at the top of his/her art or profession.
    What I am saying is that it is a bit strong for someone who is
    neither a good songwriter nor performer to denigrate a tryer
    when they themselves could not do half as well.
    As for tact it takes a great deal of thoughtful words to get the
    message across without seeming downright destructive and at the
    same time offering positive advise, especially if the critic is
    not well versed in the art of folk music.
    From what I have seen of your contributions to various items I
    cannot imagine you would ever be tactless enough to say to
    someone,
    "I`m Ron, I thought your song was lousy, the sentiments were
    sloppy, the tune was dull and your singing left much to be
    desired. Now don`t come back till you`ve cured everything"