Phoenix
It is a good old (actually, Middle) English word, but it did not come about as an acronym. As explained on dictionary.com:
Word History: The obscenity fuck is a very old word and has
been considered shocking from the first, though it is seen
in print much more often now than in the past. Its first
known occurrence, in code because of its unacceptability, is
in a poem composed in a mixture of Latin and English
sometime before 1500. The poem, which satirizes the
Carmelite friars of Cambridge, England, takes its
title, “Flen flyys,” from the first words of its opening
line, “Flen, flyys, and freris,” that is, “fleas, flies, and
friars.” The line that contains fuck reads “Non sunt in
coeli, quia gxddbov xxkxzt pg ifmk.” The Latin words “Non
sunt in coeli, quia,” mean “they [the friars] are not in
heaven, since.” The code “gxddbov xxkxzt pg ifmk” is easily
broken by simply substituting the preceding letter in the
alphabet, keeping in mind differences in the alphabet and in
spelling between then and now: i was then used for both i
and j; v was used for both u and v; and vv was used for w.
This yields “fvccant [a fake Latin form] vvivys of heli.”
The whole thus reads in translation: “They are not in heaven
because they fuck wives of Ely [a town near Cambridge].”
However it came about, it is a useful and versatile word, isn't it? 
-- Modified on 10/13/2004 3:29:24 AM