Back when I use to work at the club, I saw some horrific shows. Everything, Emmet Swimming (most notably for how TRASHED the crowd got), the Bogmen...they were all the pits. I think the worst was God Street Wine with the Cravin' Dogs. I had to go the dressing room for the Cravin' Dogs, and the b.o. coming out of that room could have risen the dead. God Street Wine was probably the worst because they played for about 2 hours and they wouldn't leave their dressing room...so by the time I got home it was about 5:00 am I think. For various reasons I also had to suffer through Chumbawamba not once but TWICE!!!
As far as bands I wanted to see, the worst was probably the Jesus and Mary Chain's last tour in 1998. It was a disaster. They didn't want to be there, everything was falling apart (including amps). I walked out of Tricky once too...that was pretty sucky. Sonic Youth in 1998 was also really disappointing. They're pretty much a hit or miss band in concert, but most of the tiem they're good. When they're off though they are OFF. At the old club I would say the worst show was the Orb. That show just never got off the ground.