smallstonefan
U2. Probably didn't help that I had the worst seats in the venue (literally TOP row in the upper upper bowl) AND Kanye West opened for them.
 
That was the one and only time I let a friend get the tickets. 

That sounds like when I went to see Garbage in 2002.  Friend told me he got pretty good seats, but ended up in the highest row in the corner.  Unlike U2, it was a good show and they had a decent opener (Abandoned Pools).

For me that would be Yes in 2015.  Chris Squire had just died.  That wasn't the problem.
 
Billy Sherwood actually did a decent job.  Steve Howe, on the other hand, had several moments where he seemed to be confused.  There were a few moments in "Siberian Khatru" where he seemed unsure of what part to play.  Then in "Owner of a Lonely Heart", he seemed freaked out when his harmonizer kicked in for the solo.  You might think that having to play that for the last 20 years, he might have figured it out by now.

Worst "Band" that ever saw would have to be Tangerine Dream. Saw them "Live" at Coventry Cathedral in 1975 in glorious "quadraphonic sound". Listening to paint dry, not watching, would have been more exciting experience. I didn't doubt these guys talent in the production of that genre of electronic music but as a "live" viewing experience it left a lot to be desired. At no point did i ever feel the urge to remove my backside from the seat and have a dance .... :-)

In '82, I saw a comedian open for Asia at the Auditorium Theater in Chicago. It was like watching a slow motion train wreck. I mean, the kind that involves a tanker full of toxic waste, a truck carrying nitroglycerin, and a freight car full of hog manure. Actually, that would have been a much better opening act.
 
Many years later, I saw I Mother Earth open for Dream Theater. It's not that I Mother Earth were terrible musicians. They played well and sang in the general proximity of the right key. They were just boring. Each song sounded lamer than the one before. Dull. Monotonous. After a few hours (relative time), I realized that I would have preferred to listen to a poetry recital at the Mount Tedium Junior High School for the Criminally Insane. In between obnoxiously insipid songs, the vocalist started screaming at the crowd for not listening to them, thus demonstrating the full extent of his intelligence. I wish they had hired a comedian instead. 

Led Zeppelin - 1977 - "Presence" tour in the Kingdome in Seattle. I was a big Zep fan, but the Kingdome was a 60,000 seat concrete toilet bowl with horrible acoustics. If it wasn't for the fact that I was very familiar with all their material, I would have had no clue what they were playing.  Not to mention, seeing any act in a place that big is a waste of time.

 
Fortunately, I saw them several times on earlier tours in Vancouver, so I didn't feel like I missed out on seeing something special.