I've long hated the truly pathetic, maximally monotonous, and self-important Metallica. However, I've long been fascinated by the absurd extremity of Danish and Norwegian metal. So, although I find the music of Mercyful Fate unbearably bad, I took a detached interest in them and their lead singer, King Diamond. I've now changed my view: they all suck.
Here's a clip of Metallica being joined on stage by King Diamond for a medley of Mercyful Fate songs. This is truly awful. Note the exceedingly low-quality air guitar chops of Diamond. No metal singer should ever be permitted to play air guitar. Ever.
Prepare to be bored.