ask a scatterbrain: non-productive relationships

So, a while ago we had a discussion on how, from the grad student perspective, you might go about changing advisors or switching people off committees, etc. Here is a question from the other side. If you’re working with a student and the relationship isn’t productive, what do you do?* What is the best way to convey this to the student, and either make it productive (or, as is more likely the case) encourage them to look elsewhere so that they CAN have a productive relationship with an advisor/committee member?

* To students who work with me: this is not a not-so-subtle hint about you, nor should you panic that I’m about to drop you like a hot potato. It’s a question that’s come up in a series of conversations over the last few years, and I figured I’d ask it as part of this series. So worry not. As you all probably know by now anyway, I’m very up-front.