I'd say he made that one up, but it is a curse of sorts. About 65% of Japanese are atheists, only practicing the ceremonies and holidays of Buddhism and Shinto because of tradition. So they don't normally curse (condemning someone to Hell or using a name of a god), but they do have bad words.
Concerning all of the words about bodily functions, etc., that he thinks are okay to say, he may not realize that his wife would frown on them. Man and women have different sets of vocabularies in Japanese. Also, he would not normally use such words to a superior.
There are polite words or even euphemisms for these functions that he would use in such a case. For example, the polite word for "bathroom" (which is an English euphemism) is Ote-arai, meaning "honorable hand-washing place."
You nailed it. This is all correct, except that the suicide plane is normally Romanized as
Ōka or Ohka, pron. Oh-kah, but that's a minor detail.
The word baka (fool) is very common in Japanese, and parents even use it on their children. Unfortunately, even Christian parents do so. The translators of the Japanese Bibles, though, use a more polite word for fool, orokamono, meaning they consider baka to be slang. When you add the word for "country bumpkin" mentioned above, it becomes something very nasty.
P. S. The Chinese word for "foreigner" in the 19th and 20th century was gweilo (鬼佬), meaning "foreign devil," and I understand it is still used in Canton Province (Guangdong). However, this is not a "taboo word," but simply rude.
Thanx for the clarification. Been over 50 years since I was in Tokyo. Hirohito was still Emperor. Nintendo was still just a greeting card co. There were still portraits of Mac Arthur on some buildings. I suppose much has changed there since then !