marbles

[jimbob121]

lost his marbles

[Ashley]

The origin of the phrase is uncertain. One suggestion is that it derives from a story about a boy whose marbles were carried away by a monkey. An unlikely derivation is in rhyming slang, where 'marbles and conkers,' two popular children's games represent 'bonkers.' [[note: 'conkers' is a children's game in which the object is to break the opponents horse chestnut which is suspended on a string. 'Bonkers' means crazy]]. The expression dates form the 1920s. <'At a time when the Prime Minister seems to be losing his marbles, a Hague-Portillo alliance could be as effective and formidable as was the Blair-Brown alliance before 1997.'The Times (2 November 1999)