How do I explain to my parents that I'm an atheist?

you and me both bro, I'm in the same situation, except my mom would probably start trying to exercise the "demons" from my body. If you want to tell your parents your an atheist I'm sure they'll except it and still love you, same as before, and if they don't then screw them for not being open to other people's beliefs. I will have to do the same thing come confirmation time (roman catholic) so believe me it won't be too long until I do the same.