There's so much I could say right now, but it's all sort of jumbled up in my head and I don't know what wants to jump out first. Satan is ascendant in this world, but that doesn't mean we get to give up. Christ said that gates of Hell shall not prevail in the end.
With that being said, if anyone tries to deny the existence of God, point out how many people seem to embrace Satan. Without God there is no Satan. Therefore, the whole-sale embrace of Satan by people means that God has to exist. I would point out that the Democrat Party's embrace of the murder and slaughter of infants in the womb should be proof enough of Satan's existence, but that's my personal opinion.