John Keats wrote as follows to his sister-in-law Georgiana Keats in 1820:

"Twang dillo dee. This you must know is the Amen to nonsense....[No thief or murderer would] condescend to be a Twang dillo dee....Some philosophers in the Moon...say that Twang dillo dee is written in large letters on our globe of Earth."

Where he heard it, I dunno.