word choice - What are the origins of ド when used as emphasis, and is it always negative?

Sometimes I've seen ド as a prefix that adds emphasis to words. So saying someone is ドバカ is saying that they are much more stupid than just バカ.

I'm wondering what the origin of ド in this context is. Does it come from 度 【ど】("degree"), as in, "the degree of X is higher"?

Also, is it always negative? I usually see it attached to negative terms, but I don't know if it's exclusively negative.

Lastly, is it impolite?

Answer

In present Japanese, the usage is not limited to negative terms

ど真ん中 'right in the middle', 'bingo!'
ど根性 'strong guts'

but does not seem to be productive either (i.e., usage is limited). When it is used with a negative term, that is surely impolite, but the words listed above are not particularly impolite.

ど seems to have derived from the 18th century form どう, whose meaning is not clear. There is another descendant form どん, which developed mainly in the context of kabuki (歌舞伎), and seems to be used only for negative terms.

どん尻
どんケツ
どん引き [Recent slang]

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