There isn't really any such thing as so-called double-jointness. It's called contortion. It also doesn't mean that I have extra joints. It's just that they are a lot more flexible than ordinary. And yes, just about anyone could do it if they wanted to. So if you can't do it, it's your own fault. :)
Double-jointedness
Yes, I am double-jointed. Actually, being double-jointed doesn't mean
that I have extra joints. It's just that they are a lot more flexible
than ordinary. I'm mostly double-jointed in my fingers. Below is a list
of some of the things I can do: