The next level up from Metalgasm. The riff heard is so awesome, that your mortal ears and brain just couldn't stand the intensity, and your head just explodes from the strain.
First seen in Tenacious D Pick of Destiny
Headbanger 1 : Did you hear what happened to Bob.
Headbanger 2 : Yeah poor guy got an Ubermetalgasm while listening to Metal Meltdown and Enter Sandman simultaneously. His brains went everywhere!