There's no such thing as an atheist according to the Bible.
Romans 1:20-21,
V. 20, “For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse.
V. 21, Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.”
The ultimate reason unbelievers don't give their life to Christ isn't because of any excuse they give. It's because they love their sin more than they love God. It's hard for sinners to stop sleeping with their boyfriend or girlfriend, to give up their adulterous relationship, to be held to God's moral and righteous standards.
The ultimate reason people don't give their lives to God is because they love the darkness more than they love the light; John 3:19, And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.
Atheism is defined by Webster's New World Dictionary as, "(1) the belief that there is no God, or denial that God or gods exist,(2) godlessness."
An atheist, therefore, is a person who believes that there is no God.