if atheists think that christians are arrogants for their belief in God, then atheists would be arrogants as well for claiming something they don't have evidence for it, and it turns out to be a belief system, I would assume, but it depends on the level of atheism I suppose.
if you say God does not exist, then a Christian and an Agnostic could ask you where is the evidence to support such claim.
Atheist: "God does not exist"
Agnostic: "Evidence, please?"

Besides, I kinda agree with Anubis, in the sense that if believing and being a christian makes one happy, then good for them, it is not a bad thing, as long as they leave other people with different beliefs and lifestyles alone.
If someone says, "I don't believe that there is a teapot orbiting the sun between Mars and Jupiter," do you demand evidence for their disbelief? Our telescopes do not have the resolution to prove or disprove an object the size of a teapot at that distance, so its existence or nonexistence must be taken as an article of faith. There are a great number of highly improbable things that cannot be disproven, and thus their non-existence must be taken on faith. Do you demand 'proof' that there are no immaterial, invisible dragons in your garage? Or proof that there are no fairies in your garden that are too clever to be detected by science?