Grammar Rules, Except When it Doesn't

A: We're having a BBQ. I think you should come.
C: Where is it at?
A: Somewhere where they don’t end their sentences with prepositions.
C: Ohhhhh snap. (He’s good.)

In my defense I'd like to point out that this "rule" is a decendant from latin in order to avoid confusion. I do not believe my question was confusing.

But still, touche, A, touche.