My dad put up with a lot of crap from the JW's when my mom divorced him and took us kids away. So when he got the chance he would mess with them at the door. My favorite question he asked 2 sisters when they came.
"If the bible says a wife is to give her husband his due, then do you have relations with your husband because you love him or because the bible says to?"
This really flustered them and they offered to have their husbands come back to discuss it. He declined stating he was just wondering their thinking on this.
So what other questions could you pose that are not serious topics that would throw them for a loop?