Go ahead. Step into his den and tell him there is no God.
The roar of instant remorse should send you into last week. Go ahead, tell him he does not have a Creator. But pay attention to the thunderous reply when the breath of his nostrils graciously tells you to reconsider such ignorance.
As for me? I am just thankful that God reigns through grace today, as the greatest proof of His existence is His glorious silence, especially when met by the rebellion of the created. His word is enough. It quietly roars.
Then again, rivers, lakes, oceans, rainbows, and the stars above are rather loud nevertheless.