As queer as a nine bob note
Odd or unusual. Also used to mean homosexual.
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 queer 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 queer as a three-dollar bill".
The British version had variants; for example, 'as queer as a nine-bob watch', which would be suspect on account of its unrealistic cheapness, and 'as queer 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'.