ultracrepidarian
(adj. & n.) [ˌəltrəˌkrɛpəˈdɛriən] — going beyond one’s proper province; giving opinions on matters beyond one’s knowledge; ignorant or presumptuous critic (OED)
ultracrepidate
(v. intr.) [ˌəltrəˈkrɛpədeɪt] — to venture beyond one's scope (OED)
I could identify thousands of these people, but I bet you can’t name a single one.
The root of this word is, I suppose, crepidarian. You might think it would be crepidate, or just crepid-, but crepidate doesn’t seem to be a word in English and crepid- doesn’t seem to be a stem. Crepidarian would come in handy were one interested in speaking precisely about a shoemaker or about his effects, about things belonging to or having to do with shoemakers, and a shoemaker could in turn be ultracrepidarian were he to set about making fiddles, say, or vivisecting wombats.
But why crepidarian was pressed into service by people who wanted a word to refer in general to people bloviating out of their depth or to critics who don’t seem to know very much either about what they’re criticizing or about what criticism is or should be, that is something worth exploring, or so it seems to me.
Yet as looking into this matter promises to be more complicated than I have time for at the moment, I’ll just tell you that crepidarian comes directly from Latin crepidarius, which sounds like someone’s name, so maybe the meaning of this word derives from the name of the shoemaker who started it all, but I doubt it.
When I have something more to report about these words, I’ll just update this post and you, if you’re interested, can check back from time to time.