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: 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.
- Romans 1:20-21 (KJV)
There is no excuse. All people know God exists. There's just no denying it.
Some people will create an alternative lifestyle separate from God, so they can follow their own wicked goals. "Yes God, I know you exist, but I've created this really interesting evolution theory, that allows me to live without you, so that I can do all my wicked things".
The fool hath said in his heart, There is no God. They are corrupt, they have done abominable works, there is none that doeth good.
- Psalms 14:1 (KJV)
It's also interesting that people don't even want to give thanks to God. This seems to me the least you can do.
"Thank you Father, for creating and redeeming me".