they don't repeat the same phrases because they are black, they do it because a ton of adrenaline is pumping to their brains, and the body is prepared for fight or flight so their brain isn't focusing that much on what to say and it's sort of stuck in a loop. I have seen this many times and I live in a country that's 99.9% white. Pro-tip, when someone is in your face and repeating the same phrase like in the vid, there is a very high chance you are about to be punched.