A person who has become extremely vocal about their atheism and is trying to convince others of their point of view. Often they are regarded as an embarrassment by fellow atheists.
Sometimes their behaviour is an indication of the insecurity they might feel in supporting their belief ,especially when confronted with reasonable arguments from the other side.
Some Evangelical Atheists seek relief and vindication by lobbying to pass laws that will make it difficult for religious people to voice their opinions in the public square, or teach their beliefs to their own children.Or even to assemble together with like minded people if the assembly is on government property.(as in New York)
For others, their proselyting rage may be an indication that their beliefs are foundering and they are on their way to a radical paradigm shift ( ie Anthony Flew )
Richard Dawkins ' The God Delusion' The opus magnum of a well known Evangelical Atheist
"The God Delusion makes me embarrassed to be an atheist "
- Prof Michael Ruse