Despite what you might have heard, it has nothing to do with masturbation. Almost all healthy males notice that their penis favors one direction or the other. The curve is usually slight, and should not be cause for alarm. The direction in which it points is decided by the ligament that surrounds the corpus cavernosum (basically the blood filling tissues of the penis) which is called Tunica Albuginea. Differences in elasticity of this two-chambered organ causes slight curvature of the penis when erect.