In the United States this is typically someone who started out as a pushy judgmental Christian, surrounded themselves with other pushy judgmental Christians, then realized that God is not compatible with being pushy and judgmental and threw the God part out of their life instead of the pushy judgmental part.
You Christians are all pushy and judgmental, I would know because I used to be one. ... When are you going to realize the Bible is a myth, you moron?
-Typical atheist ramble