A person who doesn't believe anything you say can be described as a skeptic or a cynic. Skeptics often question the validity of claims and seek evidence before accepting them, while cynics may distrust others' motives or honesty. In casual conversation, you might simply call them a doubter.
An atheist, or sometimes a secular humanist.
If someone (even a 15 year old) decides not to believe that there is not a God, then that is their choice - why the need to call them anything - live and let live.
modest
An idiot. Would this person deny that there is gravity, or electricity, or chemicals, or almost anything else? After all, what is science? What is his definition of this science that he does not believe in?
A physical haunt
every person is different. Call your doc and ask. A phone call doesnt cost anything. It is important to be sure and keep taking "Pre-natal Pills"
a dolley is someone that doesnt work.
an athiest
an athiest
pacifist
You can call him/her, Non-Christian.
You shouldn't call them anything.