With Twitter I can unfollow, With Facebook I can UnFriend, How Does One "Uncollaborate"?

So - I have this friend who is in need of help.  Suppose you have a collaborator who, well, it is just not working out with.  At one point you were sympatico.  You were friends with scientific benefits (i.e., you worked together well and were friend too).  (No it is not you dear reader - it is someone else).  What do you do now?  How does one break off a relationship with a collaborator.  You might be Co-PIs on a project.  You might share students.  Or you might study the same system.  You might share space or equipment or jointly run some project.  But now you just can't bear the sight of them.

But the problem is - they still love you.  And they don't know how you feel.  What do you do?  How do you break off the relationships when there is no "unfriend" or "unfollow button"?   I don't know (really, it has never happened to me, I swear and no it is NOT you dear reader).

I have looked for an Ann Landers or Dear Abby for scientists but have no found one.  So perhaps we need a new blog or site for people to "break up" as collaborators.  Something like IBreakUp or one of these other services.  But I think de-collaborating is more complex - more like a divorce than a breakup.  Anyone out there know of services to help scientists de-friend a collaborator?  Anyone know of stories where someone had to do this and it became complicated?  Please post - I have even opened up anonymous commenting in case someone wants to use such a function.