Last nail in the coffin

As we were leaving a staff meeting this morning, a colleague mumbled, "Well, that's the last nail in the coffin!" I checked the archive and found nothing. Any help on the origin? I can see it as being both positive and negative. Which is correct?

Old wooden coffins were nailed down before burial. So the "last nail" is a negative -- the thing that finishes you off. "He got drunk at the office Christmas party. That was the last nail in his coffin."

I'm trying to think of some positive sayings for the last step in a process. Anyone?

Something along the lines of "the cherry on top of the sundae?"