religious person tells you X is true. do you believe them?
atheists deny the existance of god(s)
agnostics deny the answer can be known, but if god(s) sat down they wouldn't yell *you don't exist*.
if god(s) show up, religious people have to worry about believing in the right X or hoping that the true X is nice and doesn't take much offence that they were following that other X that doesn't really exist will all their devotion. atheists will be just wrong. agnostics only slightly wrong depending of whether they sit on the 'impossible to know' side or the 'need more information' side. how X would react is unknown.