Grease (and not just because of this production. I've hated it forever.)
"This table, he is over one hundred years old. If I could, I would take an old gramophone needle and run it along the surface of the wood. To hear the music of the voices. All that was said." - Doug Wright, I Am My Own Wife
The worst musical I've ever seen is "I Love You, You're Perfect, Now Change" its the only time I wanted to leave a show at intermission, and afterwards I really regreted not leaving.
Hmm...I hate THE MYSTERY OF EDWIN DROOD. And I think I'm the only one. Also not a fan of PHANTOM. The score has some sweeping moments and yes it's very pretty to look at but there's not much substance there. I don't know...those two come immediately to mind although there are certainly others I like less...