Aside from paying a false compliment, the phrase is often taken to simply mean to lie, but, sadly, it’s unlikely to have originated with tobacco enemas.
‘Smoke’ is the key word, with its long association with deception in English and American slang. Stage magicians do it all with ‘smoke and mirrors’ – and at various times and places, to blow smoke, or blow smoke in someone’s face could mean to lie or to boast. To smoke someone could also mean to mock them, and also to expose a lie.
Many BBC History Magazine readers will be fans of Patrick O’Brian’s novels, and will know that his Napoleonic-era naval captain Jack Aubrey constantly uses ‘smoke’ as a verb meaning to uncover a deception, as in ‘smoke out’.
But in all the slang dictionaries we’ve consulted, we can’t find any association between smoke and posteriors before the Second World War, by which time the tobacco bellows would have long been forgotten. The second part of the phrase was probably added to ‘blow smoke’ just to coarsen it, and it may well have originated with the British or, more likely, American armed forces.
There are other explanations. Our favourite goes back to the First World War when British troops would hold a papier-mâché dummy over the trench parapet to attract the fire of enemy snipers and determine their position. For added realism, the fake Tommy would have a cigarette in its mouth, and a soldier crouching below him would blow smoke out of it through a tube.
Attractive though the theory is, the dummies never had rears to blow through, as a complete figure wasn’t needed. The dummy was usually just a head with a tin helmet, and it would have been held up on a stick.
Answered by Eugene Byrne, author and journalist.