I suppose this one has done the rounds already but it has just received an award.
When searching for this, I found that Rumsefeld was quite fond of the "don't know what we don't know" formulation, albeit not in its full form as shown below.
Apparently when he is not showing that Arnie's comment about "gay marriage" being "between a man and a woman" is impossible to top, he is quite in favour of plain English. It figures I suppose.
"Reports that say something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know," Rumsfeld told a press briefing.
"We also know there are known unknowns; that is to say we know there are some things we do not know.
"But there are also unknown unknowns - the ones we don't know we don't know."
http://www.abc.net.au/news/newsitems/s1001495.htm
PE