Ultracrepidarianism is giving opinions on subjects that you know nothing about, and is thus a terribly useful word. Ultracrepidarian was introduced into English by the essayist William Hazlitt, but it goes back to an ancient story about the great Greek painter Apelles.
The story goes that Apelles used to leave his new paintings out on public display and then hide behind a pillar to hear people's reactions. One day he overheard a cobbler pointing out that Apelles had painted a shoe all wrong. So he took the painting away, corrected the shoe and put it out on display again.
The cobbler came back, saw that Apelles had taken his advice and was so proud and puffed up with conceit that he had made the great painter change a detail that he started talking loudly about what was wrong with the leg; at which point Apelles jumped out from his hiding place and shouted: ne sutor ultra crepidam, which approximately translates as the cobbler should go no further than the shoe. Thus ultracrepidiarian is beyond-the-shoe.
Anybody wishing to know my opinions on baseball, carpentry or Pop Idol should send a stamped self-addressed envelope somewhere else.
Leave it out, son.