destroy object in front of an other object?

Use Physics.Raycast.

T$$anonymous$$s example script is meant to be placed on the camera. You might want to see the ref link about how to use layermasks to prevent destroying self.

function Update () {
    if (Input.GetMouseButtonDown(1)) {
        var $$anonymous$$t : RaycastHit;
        if (Physics.Raycast(transform.position, transform.forward, $$anonymous$$t)) {
            Destroy($$anonymous$$t.transform.gameObject);
        }
    }
}