this term is used, somewhat either neutrally or sarcastically, to define a ridiculous idea or ideas that are far off ridiculous, even by the standards of most people's imagination.
boy: my teacher would look good in a Frankenstein suit for Halloween, so I'll usurp Harry Potter's magic powers, and turn him into one for ever. I don't like that teacher anyways. No need for even a costume
boy's mother: Honey, please stop living underwater. If you think your teacher is so ugly, ask him if he is related to Boris Karloff, who was the best portrayer of Frankenstein in film, or just note in your diary that you personally think your teacher looks like Frankenstein. No need to do anything radical.