If you’re considering the f-word, you must also consider a g-word: “gatekeeper.” Before YAs land in teens’ hands, they usually pass through parents, teachers, or librarians. These are the gatekeepers for young readers, and generally speaking, cussing clogs their filters. Sure, we all know teens cuss, and yes, it would be ‘real’ to write that into dialogue, but how many parents want to put the f-bomb right in their kids’ hands?
You can make a case for foul language in YA when it’s organic to the character or situation, such as warring gangstas in a dicey ‘hood. Gatekeepers might accept bad words there because they’re already letting the kids read an edgy story. But even in rough stories you can avoid four-letter words or unsatisfying substitutions by simply recasting to avoid the need to swear. Let your characters fling cutting insults or act out physically in a confrontation—throwing things, shoving, flipping the bird, etc. You can avoid “f— you”, so do. If your book doesn’t need cussing to exist, don’t endanger its existence by cussing.