For some time now, some of my on-line friends have advised me to provide a version of CassidySlangScam without the invective aimed at Cassidy and his supporters. In response to that advice, I am working on providing a glossary of the terms in Cassidy’s ludicrous book How The Irish Invented Slang with a short, simple and business-like explanation of why Cassidy’s version is wrong.
To clean someone’s clock means to clobber them or defeat them totally. This much is true. There is no agreement on the origin of this expression. Cassidy quotes an article in the Guardian by Simon Hoggart, who says ‘It means to completely disassemble an opponent, like someone laying out the clock’s component parts.’ This seems like a pretty good explanation. Other claims can be found here: http://www.worldwidewords.org/qa/qa-cle1.htm
Cassidy claims that this phrase comes from Irish:
“Cling a clog, to ring his bell; to hit someone in his head. Cling, v., to ring. A, poss. pron., his her. Clog, n., bell.”
As usual, this is nonsense. The phrase cling a clog wouldn’t mean ‘to ring his bell’. His bell would be a chlog. The phrase a clog means her bell. Also, ‘to ring his bell’ would be a chlog a chlingeadh, not cling a chlog, which is an order or imperative. As for ringing someone’s bell being a way of saying to hit someone in the head in Irish, there is no evidence for this in any Irish dictionary or text, and Cassidy merely states it as fact without offering any evidence.