My top three would be:
The guy who rides a single speed FIXED WHEEL around the Welsh trail centres.
ANY of tandem mountain bikers (I've seen a few and you wouldn't get me on one for all the tea in China).
Joint third would be DH unicycling and the guy on a DMR trailstar that beat loads of pretty good full suss riders at Mynydd Du last year.
If some one has seen a 29" fixed wheeled, single speed tandem, that would probably win.