Of the classics, I must confess to never really getting Led Zeppelin (don't think they're awful or anything, but I just don't see the fuss). Also never got The Sex Pistols (though I like a lot of punk).
More recently, I went to see Iggy and The Stooges in Dublin over the summer. They were supported by two bands... Stiff Little Fingers (rocked like a rocking thing. Absolutely fantastic). And then there was 'The Kills'. Never in my life have I wanted a band to leave the stage as much as I wanted them off. Dreadful, insipid wank.