"I was once a born-again Christian. Now I believe it’s all rubbish!"

When a person maintains that he was once a Christian, but came to his senses, he is saying that he once knew the Lord (see John 17:3). Ask him, "Did you know the Lord?" He will then be forced to say, "I thought I did!" This gives you license to gently say, "If you don’t know so, then you probably didn’t." If he didn’t know the Lord, he was therefore never a Christian (1 John 5:11–13,20).

Explain to him that the Bible speaks of false conversion, in which a "stony ground" hearer receives the Word with joy and gladness. Then, in a time of tribulation, temptation, and persecution, falls away. If he is open to reason, take him through the Ten Commandments, into the message of the cross, and the necessity of repentance and faith in the Savior.