Not read anything by Proust or Joyce. In both cases, started, but decided being able to say I'd read 'em wasn't worth the unutterable tedium of actually doing it. Ariadne summed 'em up nicely. Ditto Kerouac. Joyce had little nuggets of purely linguistic pleasure, but there was too much wading through verbal sludge to get to 'em.
Never read anything by any Bronte except some of the poetry. Tried Eliot in my book-devouring youth, but couldn't take to her. I did manage some Dostoyevsky, & even Sholokov, from my grandmothers bookshelves. I think the imagery & exoticism made them palatable, even at the age of 12. Ditto with Tolstoy.
Are the works of Iris Murdoch considered classics now? If so. they're on my "not read" list.
What else? I've never read Pamela, but didn't need to to appreciate Fieldings piss-take of it. Which reminds me - there are still Fielding novels I haven't read. Yet. And of Elizabeth Gaskell, I've only read Mary Barton.
What about classics read, but since regretted?