'The Ballad of Les Darcy' ought to be a contender, as did 'Long Black Veil'.
Twenty years ago we had a 'Worst Song' night at the Sonsmiths Club. We asked people to bring along a tape of, or be prepared to sing, their least favourite song. There was a very wide range of rubbish played that night, but 'Any Dream Will Do' from 'Joseph and the Amazing Technicolour Dreamcoat' won by miles when the audience voted.