Sometime ago I wrote about how creationist Ken Ham teaches children to ask “Were you there?” to anyone who says that some event happened much earlier than the 6,000 years that the Bible is supposed to say that the Earth has existed. The idea behind this question is that when you say of course you were not there, they will say that you cannot assert that as a fact any event to which you were not a witness.
I said that rather than give them a lecture on inferential scientific reasoning based on evidence (which they are not interested in), one is better served by using debating trickery and sophistry, since that is the game being played.
My suggestion for how to respond to the “Were you there?” question is to simply say “Yes, I was”. This is likely to stump the stumper who will not expect it. If the person says that he/she does not believe you, you can respond, “How do you know? Were you there?” Whatever argument the person presents to establish that you were not there can be countered with a variant of the ‘were you there’ question. The reason I think this is better because in order to try and prove you wrong, the person has to use the same kind of inferential reasoning that he or she was denying the validity of in the first place, in order to counter your use of their debating tactic. You would have turned the tables on them, which is always good fun.
Unfortunately, I have never had the opportunity to test this rhetorical gambit in person since the university and community that I live and work in does not have many young Earth creationists.