In the short story "The Last Wish", Geralt and Dandelion find and accidentally free some kind of a demon. Geralt tries to banish the demon by saying an exorcism (in unknown language) taught to him by some priestess. The demon immediately flees, but returns later in a state of absolute fury. Turns out that the demon is a Literal Genie, and the "exorcism" is just a prank the priestess played on Geralt, which roughly translates to "go and screw yourself". The genie had to do exactly that.