I came in here to contribute The Fan Club too. As a young teen there were parts of that book that I really liked! 
The godfather of them all. Hoo-Hah!
Aaah, Mom’s Sydney Sheldon mysteries. Or whatever they were - I only remember the sex.
Oh, but in the one the guy you thought murdered the kids was just stuck with a crazy wife who’d had a miscarriage. And there was one in WWII or whatever. I also learned that “Rhys” is not pronounced like that. But mostly, sex.
ETA - I got most of my sex ed from the World Book Encyclopedia, though - the “s” volume, of course, but also “p” for “Painting”, which had a lot of classical nudes.
Have I missed it, no one has mentioned “Lady Chatterly’s Lover” my senior school (early 70’s) had 1 copy, it always fell open at the relevant page. 
Pretty much the only reason I read Henry Miller or Anais Nin in high school.
This.
I snuck that off the library shelves, eager for the carnal delights that awaited within…
Turns out, it wasn’t that hot - but I was (and am) fascinated by the information in that book!
When I was a sophomore in high school, a classmate told me in graphic detail about a kinky sex scene in an otherwise boring book he’d had to read for English class. He couldn’t remember the name of the book, but I was dying to check it out. Flash forward to my junior year, I’m totally engrossed in The Grapes of Wrath, get to the end and realize…
[SPOILER]he was talking about the scene where Rose of Sharon breastfeeds a starving Okie after her baby has died. 
Guy was a moron.[/SPOILER]
Hahah.
Clan of the Cave Bear, and its many sequels.
I remember as a freshman in HS convincing several friends to read it.
“Dude! It’s boring at the start! But turn to page X and it’s all sex!”
heh.
This is the first book I thought of.
The Thorn Birds. Sigh.
I seem to remember that in Forever it was page 62 we all turned to.
Wifey, yes, and the Nancy Friday book about fantasies My Secret Garden.
Who knew the words
oh
the
could be so evocative, even years after reading?
This was also the first book I ever read where a lesbian couple (Max and the other woman whose name I forget) was treated so matter-of-factly, just like any heterosexual couple.
Does anyone else remember Norma Klein’s books? She had at least two where the mother came out as a lesbian and moved in with her best friend after divorcing the dad. There was one where the girl’s mom let her read Playgirl, and she bought one at the airport newsstand to read on the plane to California. I wish I could remember the name of the book.
IT by Stephen King.
OMG…the sexual fantasy books I mentioned above were the books by Nancy Friday, not Gay Talese! Amazing what 20-odd years will do to your memory…
Anais Nin - The Delta of Venus
It’s nothing but graphic sex.
I actually stole The Sensuous Woman by “J” was it, from a teen girl cousin of mine when I was 12. To my shame it was the only thing I had ever stolen but it was just too hot not to have but Oh my God! my sweet cousin wants to know this stuff. Thing was she was 15 at the time and the volume in her bookshelf was in plain view of snooping parents, maybe they didn’t care. I wonder if she thought her parents took it.
The dictionary…the big one in the school libary. That was a wonderful source.
The Group by Mary McCarthy…some very interesting scenes…my first introduction to reading about lesbianism.
Boys and Girls Together …I think by Goldman. Didn’t have much though.
The Harrod Experiment…I’m not sure by whom.
And the best, the most explicit Candida by Voltaire…I kept going back to that. I became a major fan of the Age of Reason let me tell you. And you always had the argument when caught with it…“but I thought it was a classic?”
It took this long to get to IT?
For me it was slightly different, I didn’t read it because I knew there was sex in it, but just the opposite … my best friend in high school (a girl, actually) gave me it as a gift, I have no idea why she did, I’m not much of a horror novel reader (this remains the only one I’ve read, actually), but I went to reading it.
All of a sudden, I get to one part … holy crap, there’s sex in here! (I’d found, and visited frequently, my dad’s porno stash, by that point, so it’s not like it was the “coming of age” most of y’all are writing about) And, I read on, “there’s another part with sex! And another! And in most of them, it’s kids! Younger than me!” (Needless to say, I wasn’t feeling good about my virginity at that point). Needless to say, read those parts over and over, but only read the whole book itself one or two more times (wasn’t bad overall for a non-horror fan, I must say).
Foolish me, when the TV movie came on a few years later, I had to watch it. :smack: (Yeah, like they’re going to show those parts, you moron!)
I’m convinced to this day, even though I lost touch with her years ago, that my friend didn’t know there was sex in that book.