From:
http://en.wikipedia.org/wiki/Sarcasm
Usage
Dictionary.com describes the use of sarcasm thus:
In sarcasm, ridicule or mockery is used harshly, often crudely and contemptuously, for destructive purposes. It may be used in an indirect manner, and have the form of irony, as in "What a fine musician you turned out to be!", "It's like you're a whole different person now...", and "Oh... Well then thanks for all the first aid over the years!" or it may be used in the form of a direct statement, "You couldn't play one piece correctly if you had two assistants." The distinctive quality of sarcasm is present in the spoken word and manifested chiefly by vocal intonation ...[9]
Hostile, critical comments may be expressed in an ironic way, such as saying "don't work too hard" to a lazy worker. The use of irony introduces an element of humour which may make the criticism seem more polite and less aggressive. Sarcasm can frequently be unnoticed in print form, oftentimes requiring the intonation or tone of voice to indicate the quip.[citation needed]
