The best response is to ignore them. Does anyone think they would be broadcasting their intentions if they were really going to do it? I can assure you that we have systems in place capable of taking down any missile North Korea can send our way. I also doubt, given their past performance, that anything they launch would hit a target or work at all for that matter. North Korea has not proven that they can manufacture a missile with a nuclear war head and hit a target.
U.S. zaps target in high-stakes missile shield test | Reuters