Technically, I first saw them in '89. But get off my lawn you damn kids :)
I remember when I first heard Nirvana. I didn't really think anything of them one way or another. I wasn't too impressed. The second time I listened to them though? They blew my mind. They're not really my style, which I think is why I didn't pay them much mind the first time around, but they're just the absolute perfect blend of solid and loose, polished and rough. It's no wonder why they're such a big influence on so many artists.
I remember first hearing "Smells Like Teen Spirit." We were busily listening to Soundgarden and Screaming Trees and Alice In Chains and knew beyond a reasonable doubt that within weeks, all the fuckin' sports douches and popular kids would be moshing in the halls. It was fucking depressing.