One more for you......
Ask him if he agrees in the "new light " doctrine.
Ask him if he thinks god would use people that said something would happen or come true and then didn't, like in 1914, 1919 or 1975 or where it was that said armageddon would come before the 1914 generation would pass away? Or in 1989 that the ministry would be completed before the year 2000
( The January 1, 1989 Watchtower "The apostle Paul was spearheading the Christian missionary activity. He was also laying a foundation for a work that would be completed in our 20th century.)
Wait for an answer, he will make excuses and get giddy over the new teachings.
Ask, but do you think god would use people that said things that didnt end up coming about, yes or no?
When he says yes...
Ask him to open his bible to Deuteronomy 18 verses 20, 21, 22
‘If any prophet presumptuously speaks a word in my name that I did not command him to speak or speaks in the name of other gods, that prophet must die.+ 21 However, you may say in your heart: “How will we know that Jehovah has not spoken the word?” 22 When the prophet speaks in the name of Jehovah and the word is not fulfilled or does not come true, then Jehovah did not speak that word. The prophet spoke it presumptuously. You should not fear him.’
Ok so now the animal is wounded, he will try to claim this is non applicable, it is about prophets. Have these print outs ready.
"This was the test - the coming down of fire; and the fulfillment exactly on time has proved that Pastor Russell was one of God's great reformers and prophets." Watchtower 1919 Oct 1 p.297
IDENTIFYING THE "PROPHET"
These questions can be answered in the affirmative. Who is this prophet? ... This "prophet" was not one man, but was a body of men and women. It was the small group of footstep followers of Jesus Christ, known at that time as International Bible Students. Today they are known as Jehovah's Christian witnesses. ... Of course, it is easy to say that this group acts as a "prophet" of God. It is another thing to prove it. The only way that this can be done is to review the record. Thus this group of anointed followers of Jesus Christ, doing a work in Christendom paralleling Ezekiel's work among the Jews, were manifestly the modern-day Ezekiel, the "prophet" commissioned by Jehovah to declare the good news of God's Messianic kingdom and to give warning to Christendom." Watchtower 1972 Apr 1 pp.197-199 'They Shall Know that a Prophet Was Among Them'
If he says the claims they made were not prophecies quote this...
"Some believed that the earth would end on October 21, 2011. It did not. Thus, the prophecy of U.S. radio broadcaster Harold Camping rang hollow. He predicted that Judgement Day would come on May 21, 2011 …" Watchtower 2012 Feb 1 p.25
You can't beat a little drama. so at the end...
" Do you deny that they called themselves prophets, that they made predictions and that they were wrong and that the bible said quite clearly the way to identify a fals prophet is to look for ones who make false predictions. It also said to stone them, but I'm a nice guy, so instead I will offer you a biscuit."