Juggling isn't easy. I personally have never been able to juggle, even after upward of 10 minutes halfheartedly tossing beanbags in the air, so as far as I'm concerned, it's basically impossible. This sport takes juggling and makes it so there's a guy right next to you trying to make you mess up:
These guys are seriously skilled, especially considering that you have to maintain your own juggle even after screwing the other guy up. They also show incredible restraint, as the temptation to wind up and clock the other guy across the head has to be difficult to resist.