How about a game where two people unicycle in opposite directions, then link arms such that they're riding in a tight circle. then you go faster and faster and keep going and going and going until someone gets sick or falls over or something.. that's hilarious - it's really funny trying to unicycle when your dizzy. Miek.
how about you take some harnesses of some kind, and some pads, and 2 munis, and tie the people together with a 10-foot bungie cord, and have them ride in opposite directions, and see who can pull who off the uni?