Spyder Punk, just take your responsibilities seriously. Don't think that you should be allowed the luxury of rectifying this situation at your leisure. The fact that everyone in your family was working last Saturday means that unless you all work, or go to school six days a week, that someone had a day off during the week and could have mailed the knife then.
By the way Spyder Punk, you don't need to be banned. All you need to do is to never come back here again. If you have come to hate this place so much, that would seem to be the best solution. Even if you do this, make sure you send Dave back his knife. There are legal actions that Dave could take against you if he so wishes, so live up your obligations.
Dave, I am not sure if eighteen is the legal age to purchase a knife in all states, but I suggest that you make it a requirement from this point forward that anyone wanting to get in on a passaround be of age. If some states have a minimum age of nineteen, or whatever, then make that the minimum age for anyone to get involved in one of your passarounds. Also, get anyone that wants to take part to send you an email stating that they are of age and that they will not hold you responsible for any injuries that they may get from the use of the knife.
This may seem like a pain, but to me at least I would have no problem supplying providing such an email. I would be after all, getting the privilege of trying this knife and should therefore be willing to provide whatever guaranties that the person sending out the knife requires. If not, then tough luck, I just won't be able to take part in the passaround.