The story
Unknown. Probably of Irish origin. five conjectural etymologies * Notes & Queries, 3rd series, volume 1 (8 March 1862), page 189 posits a connection with "down the khud", supposedly used of a person falling down a precipice in the Himalayas. * Cassell's Dictionary of Slang (1998) suggests falling off the raised bank of a bog into muddy water. * Bernard Share (Slanguage, 1997) suggests a link to "The Banks of my own Lovely Lee", a Cork anthem nicknamed "De Banks". See also: * Laurence Urdang, Walter W. Hunsinger, Nancy LaRoche, Picturesque expressions: a thematic dictionary (1985, →ISBN), page 571 * The New Partridge Dictionary of Slang and Unconventional English (2006, →ISBN), volume 1 A–I, page 646
Etymology from Wiktionary, CC BY-SA 4.0.