This jumble involves the word nail and perhaps vampires? It is a mash up of “hit the nail on the head” (to get exactly right) and “the final nail in the coffin” (an event that ultimately leads to the failure of a situation or event that has already begun to fail). Also in the mix is probably “another nail in the coffin” (something that will harm or destroy someone – e.g., cigarette). Certainly the common word “nail” is the culprit here, but also the phrases conjure up the image of hitting a nail on something. For me, the image of the wooden stake (nail?) being driven in the heart of a vampire might be adding to the mix-up. A big thank you to Lou Holtzman, who heard this from a co-worker and immediately send it to Malaphor Central. That was the right thing to do, Lou; otherwise you would have forgotten it, as the best malaphors are fleeting thoughts.