The phrase “I just want to be friends” should never be used when rejecting someone who has romantic or sexual feelings you don’t share. Friendship is a wonderful thing, but it can’t be real if it is used as a consolation prize for the person whose interest in something beyond that, when you are turning that person away. The worst thing is that it can sound, to the person hearing it, as if what is being said is “I’d like you to hang around and watch me get into a relationship with someone who I DON’T regard as pathetically inadequate, just to show you how delusional you were to think you could ever possibly have had a chance with someone like me”. Some other phrase, something like “Thanks for the compliment you’ve paid me by expressing your interest in me in that way(note: I’m only suggesting this kind of phrasing would only apply if the person you are rejecting actually WAS respectful; if the person was a dirtbag, I’m assuming you wouldn’t say you wanted to be friends with them), and I’m sure you’re a perfectly nice person who has a lot to offer someone, but I’m not feeling towards you what you seem to be feeling towards me. You’ve done nothing wrong in seeking this, but it’s just not the place I’m in towards you and I don’t to give you mixed signals or make you think something is possible between us that isn’t. I’m flattered that you were interested, I wish you well and I hope you find someone, because you surely do deserve to”. Coming up with something like that-and probably in a less wordy form-would be far more appropriate than using friendship as the “Miss Congeniality/Good Sportsmanship Award” of dating.