From Don Hawkins, Flambeau at Darkcorp.com. Kregel Publications, 1999, p. 98—
Like tart cherries in a cherry pie, humor is what gives sarcasm its unique torch. Otherwise, it would simply be called anger. There's nothing wrong with anger, of course, but sarcasm provides our clients with the opportunity to become angry, even vindictive, without appearing that way. It's a lot like the carefully patterned camouflage jackets some of your clients wear when they go hunting or to war.
