To get the Breast Milk Stab, you need to strafestab. What is a Strafestab? It's when you strafe from a soldier rocket and stab the soldier. To strafe you need to Jump and Crouch before the rocket hits you. You'll need to practice a bit before doing it in casual. Dont use the kunai because you will 99% of the time die because of the Rocket damage. Hope i helped anyone