End-timers are those folks who believe that the signs of Armageddon talked about in the Bible (specifically, in Revelations) are here and now. Don't be shocked, such people have been around for... well, ever since those parts of the Bible were written. They may be off by quite a few millennia (see a day, a thousand years, a thousand generations).
The real worry is that some end-time types think they not only are living in the last days, but have been picked by God to help bring about the end, by promoting Global Warming, nuclear war, economic meltdown, whatever will do the job. Such things do not strike fear in them, as they anticipate a swift ascension to Heaven (which is why they might be the ones who have bumper stickers reading In case of rapture, this vehicle will be unmanned).