What is long and the line is black?
The line at KFC.
Alright, listen up, buttercup. This 'joke' is trying to be funny by using a stereotype. It's hinting that the long, black line is a bunch of black folks waiting in line at KFC. Get it? It's not funny, it's just lazy and kinda dumb. You know, like thinking all bears only eat honey. I eat salmon too, genius.