I got my HTC Vive only a few days ago and I redeemed the fallout VR code. I've now realised that I'm not going to play it and was wondering if it would be possible to transfer it to my friend?
Unfortunately, no. If you already redeemed the Fallout 4 VR key on your Steam account, it, like all other Steam keys is irrevocably locked to that account.
However, all is not lost, you can enable Steam Family Sharing and allow them to play the game: http://store.steampowered.com/promotion/familysharingThank you!