I presume that this is facetious, but it's not too far off the mark. See this other great Nuclear Secrecy blog post, "In Search of a Bigger Boom":

http://blog.nuclearsecrecy.com/2012/09/12/in-search-of-a-big...

The scientist Edward Teller, according to one account, kept a blackboard in his office at Los Alamos during World War II with a list of hypothetical nuclear weapons on it. The last item on his list was the largest one he could imagine. The method of “delivery” — weapon-designer jargon for how you get your bomb from here to there, the target — was listed as “Backyard.” As the scientist who related this anecdote explained, “since that particular design would probably kill everyone on Earth, there was no use carting it anywhere.”