[JSoet]

Similar, but more similar to lots of the people mentioned in the original post is the german phrase "Gefährliches Halbwissen" or 'dangerous half-knowledge': when you know just enough to seem knowledgable about a subject, but actually have a very basic surface knowledge.

(ps. I'm not a native german speaker, so sorry if I misrepresented the phrase, but this is how it was explained to me)