Often used to invoke shock into an unwitting victim's heart.
2) Can be used to determine any potential sexual relations with the other person in the conversation.
Girl 2 - "Are you fucking me?! He looked like George Clooney and Brad Pitt's love child!"
Girl 1 - "Am I what? Uhh.. Huh?"
2) Boy - "Clueless was shit, man. I don't know why you girls like it so much."
Girl - "Are you fucking me?!"
Boy - "I wish!"