1) The reason the Mythbusters couldn't replicate the feats of a true ninja is because only a true ninja can do them. The reason that the ninja they brought in couldn't do it either is because he's not a true ninja, because true ninjas don't exist anymore, and even if they did, they wouldn't deign to appear on television because they're too busy walking on water and deflecting bullets with their mind.
2) The same is true of cowboys, only they don't deflect bullets with their mind. They fire them.
3) Despite direct evidence that a particular urban myth is impossible, it totally happened to one of the commenters and the Mythbusters just didn't properly replicate the exact conditions under which it happened. Crucial elements they left out involved the exact make/model of device, the precise angle/trajectory/velocity of its travel, and the fact that it happened on a full moon in Transylvania. Unless they retest the myth under a full moon in Transylvania, they can't call it busted.
4) The commenters always know more about guns, cars, and explosives than the Mythbusters. Every single one of them.
5) The reason that Jack Burton could shoot a lock off a door and the Mythbusters couldn't is because Jack Burton's guns gain additional speed from surfing on the sheer current of awesome that Kurt Russell radiates at all times. (Okay, that's just my explanation.)
6) The moon landing totally didn't happen. Wake up, sheeple!
7) For a show that demonstrates the basic scientific principle of submitting a hypothesis to empirical testing, Mythbusters sure attracts its share of pseudoscientists.