In the Philippines, you say it after you said something dirty.
ex (balikan mo na, rupok ka diba?):
Jennie: Kumain ka na ba? (Have you eaten yet?)
Jungkook: Kainin kita (I'll eat you)
Jennie: eh!
Jungkook: rawr
(sila kasi madalas iportray as horny tsk!!)