sarcasm

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A cutting, often ironic remark intended to express contempt or ridicule.
• noun A form of wit characterized by the use of such remarks.

from The Century Dictionary.

• noun A biting taunt or gibe, or the use of such a taunt; a bitter, cutting expression; a satirical remark or expression, uttered with scorn or contempt; in rhetoric, a form of irony; bitter irony.
• noun Synonyms Irony, etc. (see satire,) taunt, fling.

from the GNU version of the Collaborative International Dictionary of English.

• noun A keen, reproachful expression; a satirical remark uttered with some degree of scorn or contempt; a taunt; a gibe; a cutting jest.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable A form of humor that is marked by mocking with irony, sometimes conveyed in speech with vocal over-emphasis. Insincerely saying something which is the opposite of one's intended meaning, often to emphasize how unbelievable or unlikely it sounds if taken literally, thereby illustrating the obvious nature of one's intended meaning.
• noun countable An act of sarcasm.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun witty language used to convey insults or scorn