From what I know, aids is a virus which doesn't survive well without a live host. This is why aids is not airborn, you can't get it from touching and you can't get it from a toilet seat or any of that nonsense. If you washed it and soaked it in iodine I wouldn't worry.
Who was this friend anyway? If it is someone close to you, can't you just ask them if they have aids? Also if it is a stain it could be rust or something. If you are that worried just throw the razor away sheesh.