Every parent knows that when a child turns teenager, he or she will keep negating what the parents say, for no obvious reason! The psychologist will say the teenager is cultivating his ego or personality, and the grandparents will say he will grow out of it. The double negation of Zen Buddhism is worse. Like the x-illusion statements that I mentioned two posts behind. A high-school kid of average intelligence can blow the mind out of an enlightenment seeker! Truly he can, like an old Zen-master with a losing mind keep striking the heads of his students, remember the act but lost the essence.
Zen Sixth Patriarch Master Hui Neng (慧能) had this experience, as mentioned in the Platform Sutra (六祖壇經). When he first met his student, the future great master Shen Hui (神會), the latter was a thirteen year old kid, very learned in Buddhist texts and boisterous as any teenager. On their first meeting, the teenager challenged the wisdom of the Master. The Master returned back, hit him three times with a stick and asked "Pain or no-pain". He answered, cautiously (and wittily): Pain and no-pain (BTW, double positive has the same effect as double negative).
The Master replied: If you feel pain, then you bear a grudge and you're therefore not enlightened; if you don't feel pain, you're like a piece of stone without compassion, you won't be enlightened.
Of course, the Master was not competing on wittiness, but just wanted the kid to be more humbled. I would say on the one hand humbleness is important, but on the other hand, one shouldn't be intimidated by the apparent irrationality of the Diamond Sutra, and certainly one shouldn't be intimidated by one possible average intelligence high-school kid pretending to be an enlightened master. The guru (or buddha) is within each of us, as the Buddha told us many times.