Sarcasm:
Sarcasm involves bitter, caustic language that is meant to hurt or ridicule someone or something. It may use irony as a device, but not all ironic statements are sarcastic, that is, intending to ridicule. Sarcasm can be witty and insightfu


Example:
http://www.youtube.com/watch?v=Jvwqel6Ncd0l.


Explanation:
Squidward uses sarcasm while talking to Sponge-bob, Sponge-bob is oblivious to the sarcasm, which can be seen as one purpose. Sarcasm is used to make someone look less intelligent, or to make fun of something/someone.