Well of course I would tell him that - if given the opportunity to do so. In fact I tell him that now.
If I am expected to believe in God without having any reason at all for doing so, I find that an entirely unfair situation to be in (although one that a God could create if He so desired) Aside from that though, I don't think that is what God requires. God will usually prompt a person that he exists. I suppose this is why Christians will say that it is God that does the work in peoples hearts and not men.
Either way, I'll stand by the fact that I feel I should have reason to testify as I do. I hold what I like to think is a reasonable faith.
I know many hate the Christians here posting bible verses on this thread, but I thought I would make an exception in the case of discussion between two of us. Only really talking about verse 15 here, but I don't want to just cut the sentence short, so I will quote verse 16 also