I would probably have to say grindcore. I know it's supposed to be structure-less, but that just results in noise to me and I can't find a shoe-in to the genre. That being said, you can stick "core" on pretty much anything and just get a more frenetic version of the genre, which is alright by me! I can take or leave things like happy hardcore, but I don't tend to come across them too much.

As an aside, I have a Romeo and Juliet style relationship with Brutal Deathcore - awesome name for horrible, horrible music.