Definition:
Sarcastic - saying the opposite of what one means, mocking, understated irritation.


Example:
"Yes I have a pair of eyes," replied Sam, "and that's just it. If they was a pair o' patent double million magnifyin' gas microscopes of hextra power, p'raps I might be able to see through a flight o' stairs and a deal door; but bein' only eyes, you see, my vision's limited.”
~ Charles Dickens, The Pickwick Papers


Explanation:
In this passage, the character of Sam uses sarcasm to very good effect in a response to another character. He names off a ridiculous device that he might use to see better, using inflated and made-up words to overstate the way in which he would use such a device. He also uses understatement when he says that his vision is limited, because of the fact that he “only” has eyes. This is obviously not a serious response, but he convey a sense of sarcasm because he says the opposite of what one would expect.