Term used over 60 years ago by my father whilst employed in a reserved occupation as a locomotive fireman during 2nd world war. Your definition misses the part labelled "fuck off" rapidly, probably whilst in danger in Darwin as it was being bombed.
n. Defungeration is the art of skillfully bullshitting. Often useful when talking yourself into and/or out of a tricky situation.
It is often used to befuddle, mystify, bewilder, perplex, baffle, confuse, bamboozle, wonder, mull, brood, ponder, stump or puzzle others.
Matty VB defungerated to Sam and Hamish by proclaiming that the Scottish monarchy decend from migrants of the Pitcan Islands.
Sam used his powers of defungeration for evil when he told Rosie he couldn't be with her because he had to immediately fly to Sweden to see a man about a dog.
Noun; De-fong-gal-ate. When a person or people leave without any notice whatsoever. One does not necessarily have to leave the premisis to achieve this, they may just go to bed without any warning. Is useful when its too hard to say goodbye or goodnight to whoever is present. By definition, you cannot tell someone you are going to defongalate, because it then would not be defongalation.