The worst show someone took me to was a friend dragging me to a Dave Matthews concert at Nissan back around '96-'97. We had a deal if I went with him to that he'd be my ride to Tool (somewhere in MD, probably Baltimore). I hated the show, it went on for ever, and then my "friend" welshed on driving me to Tool. A very lame experience.
I don't think my wife ever took me to a bad show. Good live music was a huge part of our courtship and still is a big part of our life together. I know I've taken her to a few she didn't care for though. She was pretty vocal about not really needing to see Page Hamilton's side project Ghandi twice. But at least she was nice enough to go with me for the ride to Baltimore for that second show.
@K8teebug - That Screaming Trees/Soul Asylum/Spin Doctors show at Hershey Park was one of my first concerts too!