I know I'll get slammed for this, but John Cale (opening for The Creatures) - I believe it was the summer of 1998.
I just couldn't stand him.
Also, Jill Sobule (opening for Lloyd Cole). Though she did make me laugh.
The worst *experience* at a show at 9:30 was The Cult (can't recall when that gig was). The band themselves were fine - it was the audience that was psycho - full of testosterone/high-wired guys (I believe the ratio was something like 6 guys to 1 girl at that show) - including a guy who burned me with his cigarette and then said, "Why did you put out my cigarette?!"
Cheers
DJ Medusa.