Rotating to opposite direction of parent

In a 2D environment, I want to rotate an object to face the opposite rotation of a different object - that is a 180 degree rotation from the target.

For the same rotation I used

transform.rotation = Quaternion.Lerp(transform.rotation, enemy.transform.rotation, rotationSpeed * Time.deltaTime);

To do the opposite, I’ve tried

transform.rotation = Quaternion.Lerp(transform.rotation, Quaternion.Inverse(enemy.transform.rotation), rotationSpeed * Time.deltaTime);

Which is doing the same thing.

Check this answer

http://answers.unity.com/answers/1304445/view.html