Why do some white guys act like black guys?

For years I've seen black guys in movies, on TV, etc. waving their arms and hands around making all kinds of gestures with their fingers, talking more chit than a japanese radio. " know I say'n, aight,see I say'n" that kind of crap. I just attribute it to their rythm thing and thats that. But when I see a white guy doing it I laugh my azz off. Why can't these guys just be normal? It must take some effort to put on the clown suit and act like a mindless yak with no sense of direction in life whatsoever.Do they think it makes them look cool or what? But what they hey? Atleast they make me laugh.