I try to start with personal experience. I tell them I graduated from high school in 1968. I asked a JW student before graduating what his plans after high school were. He told me there was not enough time to get a college degree and that if I did not become a JW by 1975 I would be destroyed at Armageddon. I told him he would wake up in 1976 with egg all over his face.
Then the jws usually start fumbling about how some individuals carried things too far. That's when I would ask why JWs were looking forward to 1975? Why were jws lauded for selling their homes in the late 60's and students warned it would be dangerous to pursue post secondary education?
In Watchtower literature, wasn't there an historic pattern of prophetic speculation and false predictions about the end of the world? 1914, 1918, 1925 and the millions campaign where millions were promised to survive into the new system in 1926...
Do Witnesses still believe that many of those who saw the events of 1914 will still be around to witness the inauguration of the new system of things? Weren't JWs saying that such was God's promise. Awake masthead 1980 - 1995.
Do you think those who trusted Harold Camping should have continued to put their faith in him if he came up another sure date after his first prediction was totally off base? Of course not... so how do you expect me to put my trust in incompetent men in New York who claim to be led of God but have no idea what they are talking about?