During interviews or debates, Joe Biden is often addressed as Mr. Vice President or referred to as Vice President Biden. This sounds very odd to my (Dutch) ears; nobody would address a former (prime) minister by a political position they no longer have. Even for royals, our former head of state is now a princess and not a queen anymore.
Is there any kind of law in the United States which regulates this, or is this just some kind of tradition/habit? If the latter, how and when did it originate?