My thanks to commenter Billjac for bringing up H. G. Frankfurt’s On Bullshit. I found an excerpt (right here; warning, it cuts off in midsentence) and someday I may read the whole book. The excerpt, at least, is very good and taught me a lot.

First thing, I’d said that Frankfurt, in giving his concept the name “bullshit,” simply  “slapped on” the term. No! “Bullshit” is most often used to mean something very broad, namely wildly and obviously false statements, but it is also used often enough to mean exactly the concept that Frankfurt has in mind. As far as I can tell, no other word is used for that one idea, so what can you do? Out of stubbornness, I’ll refer to the Frankfurt-identified style of bullshit as “b.s.,” but no, he was not at all arbitrary in saying “bullshit.”
More later, I guess, but I’ve got to run.