This sort of thing ain't gonna fly with black people, though. Especially in the United States where that phrase has been used to marginalize black people along with other people of colour. Black people combat the 'ol "they all look alike" mantra by adopting one of their own: "Doin' me". "Doin'" oneself allows a black person to assert his or her individuality without actually having to do anything but say the phrase. Try it!
"I'm doin' me." Don't you feel your individuality becoming more pronounced? Try walking outside! "I'm doin' me." Now everyone knows there is no one in the world like you, even if you sort of look like that other guy from work except with a slightly larger forehead.
But why do black people love to do them? Because it's a form of boasting, of course! The #1 favourite activity of all black people. Doin' me in itself, it implies a degree of flyness and realness, which is important to black people.
Black people love to spread this ideology to others. If a black person ever tells you to "do you," take it as a gesture of respect for your individuality.