The reference from Life, the Universe, and Everything refering to "The most gratuitous use of the word Belgium" exists only in the American version of the book.
In the original English version, the word is actually fuck, but it was judged that (for some odd reason) the American audience for the Hitchhiker's Guide books wouldn't be able to handle seeing that word there, and so Adams had to write an extra page and a half about "Belgium" instead.