Silliest sport that is nevertheless quite very impressive: BMX is a contender (it just seems so random), synchronised swimming too (obviously) and you have to respect a sport (modern pentathlon) designed to test the skills of a nineteenth century cavalry officer, but nothing comes close to rythmic gymnastics. I find it bizarre that this is a sport, let alone an Olympic sport, but done right, it is quite something:
http://www.bbc.co.uk/sport/olympics/2012/sports/gymnastics-rhythmic