noun which may take the genitive case particle 'no'
worst ... of one's life
Used as a no-adjective to describe the worst experience, event, or thing in someone's life. Often appears in phrases like 人生最悪の日 (the worst day of one's life).
That day was the worst day of my life.
I made the worst mistake of my life.
最悪 means 'worst' in general, while 人生最悪 specifically means 'the worst in one's life'.
best ... of one's life
Compound of 人生 (life) and 最悪 (worst).