Japanese for "What?"
You're always hearing this in anime and reading it in manga, and it's basically a simple response to anything confusing, offensive, or mysterious.
Can be used in virtually any situation. Plus you sound all cosmopolite if you can speak in Japanese.
Trans: I beg your pardon?
T: Did you just say what I think you said?!
3) "Nani kore?"
T: What is this?
T: This is all so mysterious and intriguing...I wonder what it all could mean.
When your girlfriend / girl is very protective of you or think's every girl want's you.
Guy2 - "Ah damn man, you got a nani!"