Haha, that's funny!
But I actually think it is not the child that decides on the nickname but the parents- and this is what I dislike about it. And it also doesn't make sense because why do you even give your child a name when you call him very different anyways?
If you really love a name and think it fits your child perfectly, you should name him or her that way. If there is some kind of nickname that comes to your mind once he or she is born, this is perfectly fine with me.
But I don't think that a nickname should be decided on before. A nickname is very personal and needs to really fit a person and their personality.