Hey now, I liked reading all those old books back in school - it was just doing the assignments on those books I didn't want to do.
But, serious answer now - most fantasy books, honestly. I love fantasy novels, but... fuckin' christ, are so many of them just riddled with 100-year old cliches. Nothing takes the wind out of my sails faster than picking up a fantasy novel, reading a chapter of it and going 'Ah, Heroes Journey #1137, excellent. And I'm guessing Lord DeathMurderSkull is the bad guy nobody suspects, right?'. I remember a friend loaning me a bunch of fantasy novels to read and I didn't even get half-way through any of them, since I could tell exactly what was going to happen from the get-go because of how cliched they were.
It's incredibly frustrating, since I'm always excited whenever I see a new fantasy series is out and about but have zero desire to actually read any of them since odds are they're probably not actually going to do anything interesting with all the old tropes and cliches that've been banging around since The Lord of the Rings.
(Weird thing is? David Eddings Belgariad is one of my favourite series of books, despite being nothing but Standard Fantasy Cliches. At least he's honest with 'em, or something.)