Well, probably the weirdest one I have, even though it's rather "obvious", is House of Leaves. But that's a relatively well-known and very much
intentionally weird book, in just about every way imaginable, so I feel like it doesn't count.
As far as "weird" in a straight-up obscure and/or bizarre sense, two come to mind. First is
The Mafia Cookbook, which includes supposedly real recipes from actual mafiosos -- what can I say, I was raised Italian.
The other is a pseudo-autobiographical, New Age mysticism, self-help...thing, written by the father of an old friend of mine. He (the father/author) is one of the strangest and most fascinating people I've ever known, both in good ways and bad ways. Beside being a multimillionaire tree-farmer, he was (and may still be? I honestly don't know) the leader of an internet cult that, so far as I can tell, combined Quakerism with a bunch of old school hippie shit.
The book is called
Something More, and begins with this guy describing one of his earliest memories from growing up on a farm in Gettysburg, wherein his arm was ran over by a tractor and he slipped into what he believed was some state of "higher being" for a few moments. To be fair, he really did get his arm ran over by mechanized farming equipment when he was little. I can't vouch for anything else.
Also, I believe he wrote a sequel called
Something Else, which I must say is a hilarious follow-up title, though I don't think it was meant to be so.
