Nickelback, of course. "Here's a song with sexual innuendo...Like it? He's another one. Like that one? Here's 12 more with the same riff." It's disappointing, because the guy has a really good voice for a rocker.
Macy Gray. Her stuff could be the best ever for all I know, I can't listen to it. That voice is like nails on a chalkboard.
The Doors (ducks to avoid flying shoes). It's not logical whatsoever because I can't really name an actual reason, but I can't listen to their music. At all.
Baby/Birdman - Worst. Rapper. Ever. How can someone essentially raise a talented lyricist like Lil' Wayne and have no talent himself? Does not compute.