Dear Wee Man and Prawngoby,
I assume that anyone considering purchasing a blue-ringed ocotpus has done their homework on the biology of the animal, how to care for it, and the dangers associated with them. If not, please see the information posted on the Ceph Page. This includes an article that I wrote for Freshwater and Marine Aquarium that appeared March, 2000.
If you already know that these animals are potentially deadly, that they are expensive, and that an adult will probably live in your aquarium at most only a few weeks, then there probably isn't too much I can do to dissuade you from buying one.
If you have already discounted the possibility that anyone else in you family such as a younger sibling, or a friend of theirs from down the street, will try to touch the octopus, then you know more about human nature than I do.
In short, there is probably nothing I can say that will convince you not to purchase one of these beasts. However, what I can do is offer my services as an expert witness to your family, or the family of someone else who might be killed by your blue-ring, should they decide to bring legal action against the person and/or business who was so irresponsible in selling a dangerous animal to a 13 or 14 year old. The risk of injury or death from the bite of one of these animals is well known and anyone trading in them should be aware of these risks. To offer one for sale to a juvenile, is, in my opinion, negligent and I would be happy to testify to this. Given the number of warnings that have been widely circulated, I suspect that a jury would agree.