Any mainstream country is horrible. I love old country (Johnny Cash, Roger Miller) and a whole lot of new and old folk music (and bluegrass: Chris Thile is the man), but this overproduced talentless generic pop with fake southern accents? It's just so ingenuine.
I also hate J-pop. The music on Street Fighter IV sounded like a kindergarten band on ecstasy.
I use to hate all rap. But Jay-Z's albums from the early 2000's were great (The Blueprint, The Black Album). Madlib and Mos Def are great too. I don't like "Dirty South" rap. The rap I like flows like A Tribe Called Quest. It's almost jazzy. Southern rap spits and is just grating.
I also hate metal. Those guys make me laugh. They seem like they have to prove to everyone just how "intense" they are. I just want to tell them to chill out and take a beach day. Metal is all about speed and technicality, and while I appreciate the talent and stamina it does require, I just can't dig the sound.
And I'm a Christian, but I've always hated Christian rock. How many manipulative ballads can you make?