tongue in cheek
It was once the practice to signal contempt for someone or something by making a bulge in your cheek with your tongue. From Tobias Smollett’s 1748 The Adventures of Roderick Random:
I signified my contempt of him, by thrusting my tongue in my cheek.
By the first half of the 19th century, the idea of speaking with one’s tongue in one’s cheek had come to mean to speak insincerely. From Walter Scott’s 1828 The Fair Maid of Perth:
The fellow who gave this all-hail thrust his tongue in his cheek to some scapegraces like himself.
And from Richard Barham’s 1842 The Ingoldsby Legends:
He...Cried “Superbe!—Magnifique!” (With his tongue in his cheek).
The adjectival form tongue-in-cheek appears in the early 20th century. From the Times Literary Supplement of 30 March 1933:
Shooting the Bull...is a tongue-in-the-cheek march through newspaperdom.
It is commonly held that this phrase comes from the acting practice of thrusting one’s tongue into your cheek to keep from laughing at an inappropriate moment while on stage. There is no evidence to support this story or the idea that the phrase originates in the theater.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2015, by David Wilton