If you want to catch someone off guard, I think a good idea would be to show up to meet them soaking wet on a non-rainy day and then interrupt, change the subject, or evade the question if they ask how you got that way.
People tend to think that someone needs to have a good reason to be very wet and become obsessed when they can't find an obvious one. They'll rarely guess that their obsession is, in the fact, the reason.
