We don’t have to be intimidated by anyone who says you can’t know that God exists. In an early letter to Christians in Rome, one of Christ’s followers claimed God could be known. He stated that “…since the creation of the world, God’s invisible qualities – his eternal power and divine nature – have been clearly seen, being understood from what has been made.”
His conclusion was even more startling. Because of this evidence that all humans could see and experience, he said, “men are without excuse” when they claim not to know if God exists. Romans 1:18-23
If that passage has been translated correctly and is true (and we believe it was and is), we don’t really need any more than that to be confident of God’s existence, do we? Rather than be intimidated by the disbelief of a friend, you can rejoice in what you’re convinced is true and the God who gave you the faith to believe.