People who don't believe in any religion. Some Atheists are just nice people who have just never found a reason to believe in a religion but others are douchebags who just because they don't believe in anything feel it necissarry to make fun or poke holes in your religion.
Atheist: ha you believe that some invisible guy in the sky made the world in 7 days
Cristian: Well you believe a tiny dot in the middle of space exploded and somehow created the universe. WHAT NOW BITCH