Tongue-in-cheek's a term used to refer to humor in which a statement, or an entire fictional work, isn't meant to be taken seriously, but its sarcasm's subtle. The origin of its usage comes from when Spanish minstrels would perform for various dukes in the 18th century; these dukes would silently chastise the silliness of the minstrel's performances by placing their tongue firmly to the side of their cheek. The Oxford English Dictionary defines it as "Ironic, slyly humorous; not meant to be take… (More on Tongue-in-cheek)