Both the antonym and variation of an evangelist, these are people or groups of people who are so opposed to religion that they will go out of their way to bash yours, whether Christian, Jewish, Muslim, or anything else. To them, religion is a brain-washing cult, and they have taken it upon themselves to spreading the 'Word of Rationality' by getting you the hell out of prayer. They are just as likely to be on the street with pamphlets and signs around their necks as Jehovah's Witnesses.
Random Religious Guy: My mom gave a five hour rant this morning.
Random Guy: Why?
Random Religious Guy: I feel asleep during church and I -
Evangelatheist: CHURCHES ARE PENS! PENS ARE FOR SHEEP! CHRISTIANS ARE SHEEP! OPEN YOUR EYES! THERE IS NO GOD! THERE IS NO HEAVEN! MUSLIMS ARE EXPLODING AND THERE ARE NO VIRGINS FOR THEM! HERE - READ ABOUT IT IN MY PAMPHLET!
Random Religious Guy: ... You're gay.
Evangelatheist: THAT'S WHAT YOU'VE BEEN TOLD TO THINK IS WRONG! CHURCH IS MAKING YOU HATEFUL! BURN THEM DOWN!
Random Guy: No, you're just gay.