I found this in the Ideas section of BordFunk.de A Wonderful designer. I think most of the ideas are rather arty farty, or already done, but this one I found both functional and funny in itself.
Idea 11 - Find your loveBuild a website that offers to find someone's perfect partner.
Try to achieve this by presenting a set of jokes and asking
whether they find them funny or not. If people have a
significant amount of matching jokes, they can contact each other...