What was this cosplay where Maekawa had a donut in front of her chest? Apparently this is supposed to be some kind of cosplay?

Which character is Maekawa trying to cosplay here?
The consensus opinion on a couple of Japanese forums seems to be that this is actually a reference to the main character's unnamed wife (referred to as 妻, literally just "wife") from the manga Uchi no Tsumatte Doudeshou (translated roughly as "I wonder if my wife is really normal") by mangaka Fukumitsu Shigeyuki beginning in 2008. There's very little information available about the manga even on Japanese Wikipedia, but from what I can gather it's a semi-autobiographical essay in the form of a 4-koma manga. The main character's wife acts strange in many ways and the story is about her various weird behaviors. The most notable thing about this manga, apart from being referenced in Denpa Onna, is that it won one of five Excellence Awards in the Manga division of the 2010 Japanese Arts festival.

Here's the cover of the first volume of the manga. You can see that the wife is dressed similarly to Maekawa and holding food (which she does frequently as far as I can tell from briefly browsing the manga).



Here's an image from the inside of the first volume with her eating a donut. I looked but I could not find an image with a toroidal donut. The closest is this donut without a hole (which are not uncommon in Japan).



I'll readily admit that I'd never heard of this until I looked for it. It was obscure enough that a lot of the users on 2channel were admitting they had never heard of it. You can bet that most of the audience of Denpa Onna didn't catch this reference. I'm not sure if it's more obvious in the novels (or if the scene occurs in the novels at all), but for anime-viewers this one very likely went over everyone's heads.