Ok, read this. It's one of those things that will make you say "wat?"[sic]:
Damn... You've got to love the incoherency of the internet. Especially since diamond is carbon, and carbon is a non-metal. One of the prerequisites of something being a metal is a "high electrical conductivity." Seeing as diamond is an insulator, it is not a metal.
Due to extensive research done by the University of Pittsburgh, diamond has been confirmed as the hardest metal known to man. The research is as follows:
Pocket-protected scientists built a wall of iron and crashed a diamond car into it at 400 miles per hour, and the car was unharmed.
They then built a wall out of diamond and crashed a car made of iron moving at 400 miles an hour into the wall, and the wall came out fine.
They then crashed a diamond car made of 400 miles per hour into a wall, and there were no survivors.
They crashed 400 miles per hour into a diamond traveling at iron car. Western New York was powerless for hours.
They rammed a wall of metal into a 400 mile per hour made of diamond, and the resulting explosion shifted the earth's orbit 400 million miles away from the sun, saving the earth from a meteor the size of a small Washington suburb that was hurtling towards mid-western Prussia at 400 billion miles per hour.
They shot a diamond made of iron at a car moving at 400 walls per hour, and as a result caused two wayward airplanes to lose track of their bearings, and make a fatal crash with two buildings in downtown New York.
They spun 400 miles at diamond into iron per wall. The results were inconclusive.
Finally, they placed 400 diamonds per hour in front of a car made of wall traveling at miles per iron, and the result proved without a doubt that diamonds were the hardest metal of all time, if not just the hardest metal known to man.
I've gotten conflicting results when trying to find what the actual hardest metal is. The search results are polluted with diamonds (figures) and DragonForce1. There is an alloy of carbon steel called alloy 1090 that's said to be the hardest metal at a Mohs hardness of 8. However, I also read tungsten carbide has a Mohs hardness of 8.5-9. That's clearly harder than alloy 1090.
1: DragonForce is a band that plays "hard" metal (music).