Parshat Vayeshev
Yosef "HaTzaddik" (the righteous) is a moniker unique to Yosef in all of Biblical history and Jewish folklore – others may be called righteous and may even have the term "tzaddik" used to describe them. But Yosef stands alone. Avraham is called "God's beloved." Yaakov is called the "Man of Truth." Moshe is called "Rabbenu" – our Master, our Teacher. None are known as "the tzaddik."
What makes Yosef unique is that when faced with the ultimate test, the ultimate challenge for a young, vigorous, hot-blooded male, he ran away, refused to succumb, and taught us a lesson for all time.