As ***** as a nine bob note

In the UK, until 1971, when they ceased to be legal tender, the brown ten shilling notes were a commonplace. They were popularly called a ‘ten bob note’ or ‘half-a-nicker’ (a nicker was a pound).

Of course, nine bob notes never existed. The date of the phrase’s coinage isn’t known, but the American version ‘as ***** as a nine-dollar bill’ dates from at least 1965, when it was included in John Trimble’s 5000 Adult Sex Words and Phrases:

Nine-dollar Bill… An Absolute Invert or Homosexual. From the inference that one is “Three times as ***** as a three-dollar bill”.

The British version had variants; for example, ‘as ***** as a nine-bob watch’, which would be suspect on account of its unrealistic cheapness, and ‘as ***** as a chocolate orange’. The latter was in use as a slang phrase prior to its influence on the title of Anthony Burgess’s novel A Clockwork Orange, 1962, later made into a film by Stanley Kubrick. Another variant was ‘as soft as a chocolate teapot’, which alluded to soft, that is, effeminate men.

See other ‘as x as y similes‘.