In multi-player mode join or make (recommended) a small
level. Bunker is good. Be a predator which has a disc when you
spawn. Throw the disc somewhere you can quickly get too and press
[F1] to change to a no disc predator. There is only one,
which is called Assault. When you spawn again, press the disc
retrieval key (default is F). The disc should actually
come to you. You will have the disc but for some reason you cannot
use it, even though the item indicator shows that you picked it
up.