Watching this clip of ABC News in the US reporting on the 2DS, I am honestly surprised that I've never heard someone mistakenly refer to the 3DS as 'three-dees'. Sure, it's wrong, but I can kind of see why someone would mispronounce it that way! Same goes for the 2DS.
But beyond that, this clip perfectly sums up Nintendo's current naming problem. Not only is the 2DS a tad confusing as a name for a console (I suspect we'll continue to see bumbles like the one in the clip, if not worse), but the Wii U and Wii continue to be confusing for people too (you catch the anchor referring to the Wii U as the Wii, right?) -- this is true even though Nintendo seems to be convinced the name isn't part of the Wii U's problem, sales-wise.
Regardless, good job spotting this, ElectricBlanketFire.