Ultracrepidarian
From Wikipedia:
Ne supra crepidam ("not beyond the shoe") is a Latin expression used to tell others not to pass judgment beyond their expertise.
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Supposedly, Apelles would put new paintings on public display and hide behind them to hear and act on their reception.[2] On one occasion, a shoemaker (Latin sutor) noted that one of the crepides[a] in a painting had the wrong number of straps and was so delighted when he found the error corrected the next day that he started in on criticizing the legs.[2] Indignant, Apelles came from his hiding place and admonished him to confine his opinions to the shoes.
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An ultracrepidarian—from ultra- ("beyond") and crepidarian ("things related to shoes")—is a person considered to have ignored this advice and to be offering opinions on topics they know nothing about.