Irish English: What is cat melodeon?

Cat (a): dreadful, no good, awful, very bad. Or for a more emphatic version, Cat melodeon (Sounds like 'melojen')
The Cat Melodeon players
Bernard Share’s Slanguage quotes Victoria White in the Irish Times calling cat melodeon “the greatest expression in Hiberno-English.” Not sure about that but it is fun to hear and use.

Where does Cat Melodeon come from?

In his book on Irish traditional music Ciaran Carson suggests it derives from the tendency of the piano-accordion players (who often refer to their instruments as melodeons) to play two notes at once.  Source

How is it used?
I have most often heard it as a yelp of protest: That  film was cat/melodeon!/Cat altogether!'

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