Real Nigga is someone who always be 'themselves',not someone who goes on killing sprees and doesnt care about anything. But, being a real nigga, being yourself means showing everything about yourself but your weaknesses, knowing them at the same time. 
It's all about being real and true to yourself. The opposite of real is fake. 
You don't have to be black to be a real nigga, but it helps. 
Being in the hood carrying a gun talkin shit is not being a real nigga, beacuse when the police come you will be crying for your mom. 

Being a real nigga is doing what ever you do, doing it best, not pretending to be a wannabe thug like everybody else

Quan Da Mon