It's quite simply the most retarded comeback someone makes when they've completely lost the argument. This statement signifies that the argument has gone to a completely immature level. Below is a hardcore argument starting with the immature statement :)
Person 1: I know you are, but what am I?
Person 2: Good question. What are you?
Person 1: Wow, you're so dumb, you don't even know what I am?
Person 2: You're so dumb, you can't even answer my question.
What you say to dumpeople that are getting in your bizness or messing with stuff they dont need to be messin with.
(thinking they know somthing when they dont )
Bill: LMAO I bet she dumped you cus u were a cheap ass!
Nick: Man Dont be dipping in the koolaid when you dont know the flavor.