I've been doing this for nineteen years
Niggaz wanna fight me? Fight these tears
can be interpreted to mean that he has killed many people in his time. In gang culture, it is a cliche to have a teardrop tattooed onto you for every kill made for your gang in a gangfight. So, "fight these tears" is his way of saying he has many "tears," or kills, and not to fuck with him.
Not a full analysis, but the lines:
I've been doing this for nineteen years Niggaz wanna fight me? Fight these tears
can be interpreted to mean that he has killed many people in his time. In gang culture, it is a cliche to have a teardrop tattooed onto you for every kill made for your gang in a gangfight. So, "fight these tears" is his way of saying he has many "tears," or kills, and not to fuck with him.