How to determine if enemy is on my left or right hand side?

I have 2 game objects. Game Object A and Game Object B. GO A is facing a direction and I want to know if GO B is on the left or right of GO A.

To illustrate my problem I made a picture:

Facing example

The red line is the direction I'm facing (the z axis of GO A is pointing that way).

So how can I determine if GO B is facing to the left or right as seen from GO A, regardless of their positions in world space?

Use InverseTransformPoint:

var otherTransform : Transform;

function Start () {
    var relativePoint = transform.InverseTransformPoint(otherTransform.position);
    if (relativePoint.x < 0.0)
        print ("Object is to the left");
    else if (relativePoint.x > 0.0)
        print ("Object is to the right");
        print ("Object is directly ahead");

You could make two raycasts, one(1) from A directly forward and one(2) from A to B, and then compare the x components of their directions (I think that it would be left if 2.x < 1.x and right if 2.x > 1.x).