It's a bird! It's a plane! It's sarcasm flying right over your head!

A retort used against someone who has just taken your obviously sarcastic statements as an indication of what you actually believe. Has the effect of both stripping the easily offended jackass of any perceived upper hand in the argument and making him/her even more furious that you had the audacity to publicly declare their idiocy.

All meaning that you, the sarcastic smartass, triumph again.

Bonus points if you point upward and actually get your victim to look at the sky before the punchline.