Ladies: how do you hint to a guy friend who might be coming onto u that ur not interested ?

I have a friend at work who I sometimes teeter on liking and I'm not sure how I come across. Anyway if you felt that conversations were getting too friendly (and it might be moving in a non-friend direction that you don't want it to go), how would you go about letting a guy know? Boldly? Hinting by saying things like "some girl will be lucky to have you someday?"