Screwtape on flippancy

I divide the causes of human laughter into Joy, Fun, the Joke Proper, and Flippancy. You will see the first among friends and lovers reunited on the eve of a holiday. Among adults some pretext in the way of Jokes is usually provided, but the facility with which the smallest witticisms produce laughter at such a time shows that they are not the real cause. What that real cause is we do not know. Something like it is expressed in much of that detestable art which the humans call Music, and something like it occurs in Heaven—a meaningless acceleration in the rhythm of celestial experience, quite opaque to us. Laughter of this kind does us no good and should always be discouraged. Besides, the phenomenon is of itself disgusting and a direct insult to the realism, dignity, and austerity of Hell.

....
  But flippancy is the best of all. In the first place it is very economical. Only a clever human can make a real Joke about virtue, or indeed about anything else; any of them can be trained to talk as if virtue were funny. Among flippant people the Joke is always assumed to have been made. No one actually makes it; but every serious subject is discussed in a manner which implies that they have already found a ridiculous side to it. If prolonged, the habit of Flippancy builds up around a man the finest armor plating against the Enemy that I know, and it is quite free from the dangers inherent in the other sources of laughter. It is a thousand miles away from joy it deadens, instead of sharpening, the intellect; and it excites no affection between those who practice it.

-  Senior Demon Screwtape, to his Nephew Wormwood

Transcribed by C.S. Lewis -  The Screwtape Letters