The phrase (with) tongue in cheek means in an ironic, or insincere, way.
The Scottish author Tobias Smollett (1721-71) used to thrust one’s tongue in one’s cheek to denote a sign of contempt in his picaresque novel The Adventures of Roderick Random (1748); the hero has just captured and handed over a highwayman and returns to the coach in which he is travelling:
When I had taken my seat, Miss Snapper, who from the coach had seen every thing that happened, made me a compliment on my behaviour, and said, she was glad to see me returned, without having received any injury; her mother too owned herself obliged to my resolution; and the lawyer told me, that I was intitled by act of parliament to a reward of forty pounds, for having apprehended a highwayman.—The soldier observed, with a countenance in which impudence and shame struggling, produced some disorder, that if I had not been in such a damned hurry to get out of the coach, he would have secured the rogues effectually, without all this bustle and loss of time, by a scheme which my heat and precipitation ruined.—
“For my own part, (continued he) I am always extremely cool on these occasions.”—
“So it appeared, by your trembling” (said the young lady.)—
“Death and damnation (cried he) your sex protects you, madam; if any man on earth durst tell me so much, I’d send him to hell, d—n my heart! in an instant.”—
So saying, he fixed his eyes on me, and asked if I had seen him tremble.—I answered without hesitation,
“Damme, Sir, (said he) d’ye doubt my courage?”—
This declaration quite disconcerted him.—He looked blank, and pronounced with a faultering voice,
“O! ’tis very well—d—n my blood! I shall find a time.”—
I signified my contempt of him, by thrusting my tongue in my cheek, which humbled him so much, that he scarce swore another oath during the whole journey.
The verbs stick, put and roll were subsequently used instead of thrust; for example, the following is from Feeling in Actors, published in The Bath Chronicle (Somerset) of 12th February 1807:
Garrick¹ roused the feelings more than any actor on record, and most probably suffered as much from their exertion. However, it is related by a medical gentleman of eminence, that on his once making the above remark to Tom King², the comedian, he received this reply:—“Pooh! he suffer from his feelings! Why, Sir, I was playing with him one night in Lear, when in the middle a most passionate and afflicting part, and when the whole house was drowned in tears, he turned his head round to me, and putting his tongue in his cheek, whispered, “Damme, Tom, it’ll do!” So much for stage-feeling! In fine, an actor may make others feel, without feeling himself; as a whetstone can work up steel till it cuts, which the whetstone never does.
(¹ the English actor, playwright and theatre manager David Garrick (1717-79))
(² the English actor, playwright and theatre manager Thomas King (1730-1805))
A satirical article, On the office and duty of jurors trying “political offences” in Ireland, published in the nationalist newspaper The United Irishman (Dublin) of 8th April 1848, contains:
Above all, they [= the jurors] must keep their countenances:—they are to listen with much solemnity to the man in whalebone³, who will set them an admirable example of gravity all the time. Semble⁴ that they are not to wink, put tongue in cheek or thumb on nose, but make believe that they consider the affair a solemn judicial investigation.
(³ = the man in whalebone wig: the judge)
(⁴ semble: it seems; a law term, from French il semble, it seems)
I have found an early instance of the current phrase, with tongue in cheek, in the speech given on 28th January 1891 at the annual dinner of the Sheffield and District Conservative Clubs Federal Union (Yorkshire) by its president, Sir William Leng; he declared that a political opponent
held out to the people visions of pensions for everybody at 65—(laughter)—of meals free of expense for the children attending public schools; and, in addition to this, he openly and corruptly made a bid for the electioneering help of the entire machinery of such trades unions as would lend themselves to the suppression of individual liberty and individual independence. (Hear, hear.) Well, all this was hollow! They would never more hear mention of the pensions at 65. (Laughter.) The hollow trick was not that of a man speaking simply with tongue in cheek, but with tongue in cheek and with cheek in tongue. (Hear, hear, and laughter.) It was burlesquing politics, and reducing them to a vulgar farce. (Hear, hear.) If he had to compete with such a man, and were as unscrupulous, he would promise to print £1 notes on perfumed rose-tinted note paper, and to send them round on silver trays every morning before breakfast to every working man, and to take the money out of the taxes. (Loud laughter, and applause.)
The earliest instance of the adjective tongue-in-cheek recorded in the Oxford English Dictionary (2nd edition – 1989) dates from 1933, but I have found one in The feud and the factions, published in The Weekly Waterford Chronicle (Ireland) of 24th November 1838:
We have been for some days past laughing at the bursting of the long latent feud in the bosom of the faction. It has manifested itself not only politically, but in the late exhibition, editorially and personally. The incident which gave rise to it was the late open revival of the Orangemen of Ireland—a body brought to life, which never died—a feat worthy of a Trinity miracle-monger. This “untoward” incident of private speculation has quite unhinged the tactics of the party. The facts are these:—
Professor Butt—a ‘professor’ in more senses than one, and who was discarded for incompetence as the editor of a Belfast Orange paper—determined, like other “fools and their money,” to try his hand at a genuine rag of the “right sort,” and “no mistake,” in Dublin. The ‘Packet’-man was an ass—the ‘Mail’-man a Papist knave, a Shawite, who trimmed his sails and turned his rudder according to signals from Peel, took hints from Shaw, and played the game of the cunning section of the faction. In short, Butt became infected with the common fallacy soon dispelled in his case as well as in others by experiment—that all the existing papers were wrong—that he alone could edit a paper as never man did, and accordingly this great professor set up a paper, which the poor fellow called the ‘Protestant Guardian.’
Well—the Protestants did not seem to regard this guardian. Like others who, before trial, fancied they had an exclusive secret for editorial success, the paper fell dead-born. What was to be done? There was in existence a boiling mass of vulgar Orangeism, reluctantly restrained by the tactics of Peel—still organised, but pretending they were not; here they were just the men for an adventurer to trade upon.— Accordingly, Butt gets up this meeting on Wednesday last, which we before noticed; there he openly revived the Orangeism which the policy of the faction would at present seem to have dissolved. The ‘Mail’ was not Protestant enough for such a Protestant out-and-out affair—its reporters were excluded; and thus the tactics of the wily Peel, of the imbecile Shaw, and the trading tongue-in-cheek ‘Mail,’ laughing at the whole pack of dupes, is sacrificed to a newspaper juggle.
It is difficult to ascertain the exact meaning of the following early instance of with one’s tongue in one’s cheek, from The Norfolk Chronicle: or, Norwich Gazette of 15th May 1790:
The late Lord Kaimes was for three or four days before he died, in a state of great languor and debility of body. Some friend came in upon him in that situation, and found him dictating to some one who was writing for him. He expressed his surprize at his being so actively employed at that time. “Why, mon [= ?],” replied he, “would you have me stay with my tongue in my cheek till Death comes to fetch me?”