Rush in Glasgow on the Clockwork Angels tour. Horrendously bad sound mix where I was sitting. This was surprising as I was a few rows directly behind the sound desk! All I could hear was drums and keyboards. I know Alex Lifeson was playing guitar as I could see it on the video screens, but I couldn't hear him or Geddy! I left after about 5 songs. On leaving the hall, the guys checking the tickets said, "don't blame you mate". Hahaha. Real shame, as I love the band.
The Seahorses supporting U2 on the Popmart tour. A busker with a backing band (albeit containing John Squire from The Stone Roses). John's guitar sounded great, but the songs and the band's overall playing were garbage! Saying that, U2 were rubbish too until around halfway through the set (once they'd got the crap Pop album tracks out of the way).
I also got roped in to seeing..... Bros at Wembley Stadium! The idea was sold to me by my ex-wife saying, "there's going to be loads of other acts on too". Turns out the other acts were SAW act like Sinitta, Sonia, and the like. Utter garbage - waste of a whole weekend