It depends on the stranger. To the two guys that were chatting me up while riding around me on beach cruisers, I keep in vague. If it's someone riding in a charity event with me, I'd tell them. But my current bike doesn't tend to interest any of the people riding road bikes, so I've never had anyone in a charity event ask me. When I get my trike, that will likely change and I'll probably shock them when they find out it costs as much or more than their road bike.