It's how "the blacks" are. They want to whoop and holler, so when you speak to a group of them, you've gotta go along with that. And you gotta change your voice so that they know that you're one of them and so they can understand you. If you don't change your accent and you enunciation, they may not understand you at all. Sophisticated, enlightened people understand all this about how you have to talk to "the blacks."