Q: I've come to disagreement w/ a friend over acceptable word choices for YA. The main cause of argument is the word "boner." The MCs are a 14 y/o girl and a 15 y/o boy. I can't see the word being acceptable, yet, she disagrees 100% with me. I realize boys, in fact, use the word but do I want my 13 or 14 y/o daughter reading it? No.BONER is about the least offensive word to do with erect penises that I can think of, and if you are writing a YA set in high school that includes those body parts, it is ok to use. I wouldn't even call this a curse, really -- in some circles, it still means "to mess up" (like "pull a boner" is the same as "boneheaded maneuver") -- and not "erect penis."
Does that mean YOU have to use it? No. Does it mean YOU have to allow your daughter to read books that contain it? No. But will it be fine to publish for high school students? For sure. Provided of course that it is right for the character, that it makes sense in context and you aren't just randomly throwing words around.
Now, of course, there is such a thing as clean YA, in which you pretty much want to avoid any blush-inducing "downstairs" business. But if you are writing scenes in which boners come into play, I am assuming that you are not writing strictly clean. (Still, you might look at a book like E. Lockhart's FLY ON THE WALL, which if I recall correctly was pretty clean, considering the fact that it takes place almost entirely in a boy's locker room... maybe there are other words you can use.)
Q: The first line of my manuscript uses the f-word twice. Line: "I can sum up my entire life in either of two words: f**k this or I quit. Maybe a grand total of four: f**k this, I quit." Would things like this turn agents away?F**K no. ;-)
I am kidding, of course. MOST agents and editors who rep a lot of 14+ YA will think a few well-chosen curse words are no problem. And yes, that includes the asterisk-free "F-bomb." You want to use it fairly sparingly, I think, but sometimes, for some characters, in some situations, there just might not be a better word. Again, you aren't going to sell these books to inspirational publishers, or to editors who focus on Clean Tween / "younger YA" fic, or who rely mostly on school/library sales - but those wouldn't have been appropriate publishers anyway, from the sounds of it.
Myself, it wouldn't stop me from reading more. But I might question whether that has to be the first line of the first page. First, because I wouldn't want somebody just glancing at the book to get the wrong idea of it. And, I sorta feel like I want to get to know a character and be rooting for them in a way before I start seeing all the unsavory parts of their personality. A couple pages in, after (presumably) we understand WHY he might have an "eff this" attitude, it will come off differently than if that is the first thing we ever learn about him. Your first page sets the tone for the whole thing, and if the whole thing is going to be like this, it might be sort of tiresome 200+ pages in. (Again - I haven't read your book - maybe it works perfectly as-is. But without context, this is what crosses my mind.)
You might also consider seeing what other YA authors have done. Lots (like the previously mentioned E. Lockhart, as well as John Green and many others) use made up slang to express the feeling without relying on the actual curse. Sometimes unique word usage actually helps create a well-rounded character, because cursing CAN be a lazy writer's way of making a character seem "edgy."