When we encounter someone really out of it at a political meeting, we commonly roll our eyes and twirl a finger in the air (like the sign for crazy, but pointed straight up). It sort of looks like a wingnut being spun loose. I don't think it was ever so andvanced as to be derived from political wings. More likely someone said "Oh man, that lady? She's a nut!" and someone else replied "She's a WINGnut" just meaing to be funny.

I can think of some Berkeley/Oakland wingnuts that don't fit to the 'extreme' end of the political spectrum (though maybe they fit to the oddball end of the mainstream). The people with the UN flags that show up at every anti-war protest, for example.