I usually cite fantasy as my favorite genre of book, although that doesn't mean I'm familiar with most of the fantasy that's been released in recent years (aside from Terry Pratchett, of course). But I still have a better answer for that question that I do for what kind of music I listen to. Probably the best term for that would be "nerd rock," but bands that are grouped under that label tend not to like it much.
In addition to not liking fantasy, there are some people who just don't like fiction, which is a rather difficult concept for me to grasp. A guy who was in a few of my classes at library school was like that. I admit I don't read a lot of non-fiction for fun, aside from comic essays. And while they clearly fall into the non-fiction category, they tend to be based largely on opinion, and not simply cold, hard fact.