It sounds like you're referencing the concept that , reflecting back parts of our own psyche, insecurities, or suppressed traits. This idea is a staple in spiritual and psychological circles, often used to turn interpersonal conflicts into opportunities for self-reflection.
What we judge or find repulsive in others often represents a "shadow" part of ourselves that we haven't fully accepted or integrated. Other People's Mirrors
We tend to project our own internal state onto the world; for example, someone feeling anxious may perceive others as being hostile. It sounds like you're referencing the concept that
Were you referring to the of people as mirrors, or did you just finish watching the 2004 film ? Other People's Mirrors