Yes, "dastardly" is pretty much a New York City thing. I think the term was made up by addisonbr in connection with an event cache with a puzzle-solving theme. To be "dastardly", the puzzle has to be in Manhattan, not at the posted coords and involve a reasonable significant intellectual challenge to solve. Once qualified, the cache would be added to a public bookmark list. addisonbr made some pathtags, and they were awarded to cachers who found certain numbers of caches on the bookmark list.
The guy organizing it has virtually left the game, to the term "dastardly" is largely historical now...