Purple

Purple: the word which never rhymes
Stands like a vampire behind closed blinds
Avoiding light, lest he be devoured
Like milk and cereal before a shower
Purple: the bane of rhyming verse
Better shut away, like the vampire in his hurst
Whatever word proceeds purple first
Never succeeds in putting an end to verse
With such aptitude as purple's curse
Be it poem, novel, essay, or journal
Purple will never cease to curdle

I think the point the author is trying to make is that no matter the level of skill applied to rhyming the lexis 'purple,' it can't be done. Ironic perhaps.