Maybe nothing better symbolized the rise of grunge, and the fall of 80's metal, than what happened in September 1991:
At the MTV Video Awards, glam metal band Poison was slated to perform. But the members of Poison began arguing onstage about what song to perform! When the band finally got going, it was horribly out of tune, with each member doing his own thing. Thus Poison delivered what some consider one of the worst performances by any rock band on national television. After the show, Poison's members hated each other so much that they broke up; ironic, because the band had agreed to appear at the Awards in order to quash rumours that it was breaking up! Big hair 80's metal crashed and burned with the fall of Poison.
Later the same month, Nirvana's nuclear bomb called "Smells Like Teen Spirit" detonated on MTV (here's yer weapon of mass destruction), and heralded a new era in music, while sweeping away the 80's.
So in this sense, September '91 was one of the most meaningful months in the history of rock.
(Lord Foul, you're probably reading my trashing of the 80's with glee...well, when it comes to big hair metal, I hate it as much as anyone else around here. It's 10% music, and 90% hair mousse & posturing. I know you think even
that's being too generous.)
