tongue-in-cheek

Example: “His review calling the burger 'life-changing' was tongue-in-cheek.”

Origin: Began as a real and quite unfriendly gesture. Pushing the tongue visibly into the cheek was a recognized signal of contempt or disbelief in the 1700s, performed where the target could see it, and early literary uses describe it as exactly that — Walter Scott used the phrase in 1828 for a character expressing silent scorn, with no suggestion of humor at all. The shift to the modern sense came over the nineteenth century, as the gesture's implication softened from open derision toward the milder idea that the speaker does not fully mean what they are saying. The physical act has essentially disappeared while the phrase survives, which is why nothing about the words now signals the sneer they originally described.