1. What one says as if to exclaim "you're an idiot" or another form of an insult that will end all other conversation on the topic without directly insulting the person.
2. A funny, covert exclamation to use when you and a friend see a person/group of people that you think are fools/generally bothersome.
*keep in mind that this is usually said in a low-pitched voice, with the hand cupped around the mouth as if you are yelling to someone who is far away.