The Beatles. Honestly, I like some of their music, but stylistically, they're too all over the place for me. Bubblegum pop to deep soulful music to flat out weird crap.
I honestly don't understand this particular problem. If you said you just didn't like them as a whole or whatever I would understand that, but to dislike them because they actually stretch themselves creatively and do different types of things is what I don't understand. That's what all bands should do.
I mean, you like different types of music I assume, I don't see how that can be a critisism you can ever level at a band.
Maybe if you said, 'they have so much of a diverse output I don't know where to begin to get into them' i could understand that, but to dismiss an artist because they diversify, I don't get it. Sorry, not trying to pick on your opinion, it just baffles me.
Anyway, out of the cultural big hitters I am supposed to like but can't stand and find boring, my top two are
The Clash - apart from Rockin the Casbah
The Jam - I have to switch off their songs when they come on the radio, they annoy me.
Led Zeppelin I can enjoy sometimes and get a kick out of, other times I can find them unimaginative bores, I really do flip 360 on those guys.
edit: forgot about The Who, I find them boring too, despite their exciting hard rock, good songwriting rep.