Anyone who has had even casual contact with the Heavy Metal fraternity will see the humour in the excellent "if you will" rockumentary that started it all off - including a lot of metal bands themselves.
I was at Reading Festival the year Black Sabbath played with Ian Gillan as vocalist, and they had the infamous Stonehenge stage set - obviously Christoper Guest was there as well!
By the way, Christopher Guest is actually Lord Hayden-Guest - he has inherited a peerage, and is entitled to sit in the House of Lords, and wonderful Lady Hayden Guest is Jamie Lee Curtis!
What a man!