This is an oldie but a goodie. I think it is from two summers ago. I cannot remember the exact subtext but it is not that important.
My sister = Y Her best friend's bf = C
C: Can I pay you back later?
Y: Sure. But ya better remember to give it back to me.* Or else I'll tell my sister to come after you.
C: Umm. Ok.
Y: She's REALLY fierce. You DON'T want to MESS with her.
I did not know whether to be pleased or insulted but I was definitely entertained.
* My sister speaks really ghetto English in informal situations (i.e. with her friends or me).