Okay, I looked up the two words in question in the Oxford English Dictionary. The word "swive" first shows up in the 1300s in Chaucer, so it really isn't Old English, at least in written texts the OED knows about, but Middle English. The "f word" comes along a couple of centuries later, in the 1500s, and it seems to be of Dutch origin. And, contrary to my hopes, "swive" (which comes from the same root as "swivel") isn't always an intransitive verb, and it even has the connotations of a dirty joke in its first usage, in the hilarious but filthy "Miller's Tale." So it seems that one of the most important, and many of us would say sacred, acts of human relationship can't be discussed for long without sliding into disrespect. A good question would be, WHY?