PH'Ultracrepidarian is a person who doesn't know what they're talking about. It's talking about things beyond the scope of one's knowledge. [Noun] Someone who talks about things of which they know little or nothing.
It is based on the Latin phrase ultra crepidam "above the sandals" from a fascinating anecdote originating in ancient Greece. The great Greek painter, Apelles of Kos (4th century BCE), occasionally allowed the public to criticize his works. One day, a cobbler dropped by and criticized his depiction of a sandal in a painting. Apelles revised his painting, which pleased the cobbler so much that the next day he proceeded to criticize the painting of the whole leg. This was more than Apelles could take, so he punished the cobbler with words that remain a proverb today. The Latin version of those words is: Ne sutor ultra crepidam "(Cobbler) don't judge above the sandals."
source:alphaDictionary.com