Many of the blindly faithful like to throw around the term of militant atheist in response to non-believers pointing out the extremism present in most religions or when we try to exert our rights to be free from someone else's religious views. Below is a video providing an interesting view on that subject.
So what is a militant atheist to most Christians? From what I can tell and what this video implies is that it is any atheist that has the audacity to open their mouths.
(H/T to EXchristian.net via Atheist Revolution)