Fundamentalists: believe 2+2 =5 because It Is Written. Somewhere. They have a lot of trouble on their tax returns.
"Moderate" believers: live their lives on the basis that 2+2=4. but go regularly to church to be told that 2+2 once made 5, or will one day make 5, or in a very real and spiritual sense should make 5.
"Moderate" atheists: know that 2+2 =4 but think it impolite to say so too loudly as people who think 2+2=5 might be offended.
"Militant" atheists: "Oh for pity's sake. HERE. Two pebbles. Two more pebbles. FOUR pebbles. What is WRONG with you people?"
(h/t to ywut)