There are certain cases, however, where adequate synonyms simply do not exist. For example, there is no direct substitute for the familiar verb "to fart". The noun "flatulence" refers to the general subject, and "flatus" is another noun for the act of farting, but there is no corresponding standalone verb. The euphamism "to expel gas" would apply equally as well to exhaling, belching, or even chortling, and a satisfactory replacement verb would not require a helper object to disambiguate its meaning. To "have" gas most often refers to NOT farting when one would prefer to do so. "To break wind" appears in my thesaurus, but is too obscure and capricious to warrant discussion here.
And where is the accepted noun to denote a single discrete instance of flatus, to replace "a fart"? Apparently nowhere. When I was a child, the accepted term in my family was "a stinky". But that expression not only awkwardly employs an adjective as a noun, it is also applicable only to stinky farts, whereas many farts are not significantly stinky and so do not deserve to be labeled as such. (While unnoticed farts may not command the attention enjoyed by the more pungent genre, they nevertheless can lay full claim to being true farts.) Certainly there is a need for accepted non-euphamisms for such a widespread field of human endeavor, one that unites us all as fellow higher organisms.
(As a side note, I am not actually certain that "fart" is a member of the ethereal list at all. Most humans appear to avoid saying "fart" in the same situations in which they avoid saying "shit", and so that may be a confirming instance of the theory that "fart" is on the list. Alternately it may be that these humans, like me, do not know whether "fart" is on the unseen list, and are merely "playing it safe". The danger with playing it safe, though, is that it may turn into a self-fulfilling prophecy that causes "fart" to end up on the list when it otherwise would have remained free.)
A more troublesome case is the rather important word "bullshit". One could substitute a much longer expression such as "a feeble attempt to deceive others about one's true motivation for one's behavior", as in "The official reasons for this war are a feeble attempt to deceive others about the plutocrats' true motivation for their behavior", but life is too short to agree to such encumbrances. And the needlessly wordy phrase simply does not convey the desired impact that is so effectively delivered by "The official reasons for this war are BULLSHIT!" The only reasonably concise alternatives are the plethora of whimsical variations within the metaphorical "farm animal" domain, such as "hogwash" and "horsefeathers". (There is also the antiquated usage of "baloney", but its use nowadays may trigger a lawsuit for meat disparagement.)
The drawback with "horsefeathers" and its bedfellows is that if I were to utter a sentence such as "The official reasons for this war are nothing but a load of horsefeathers", then I expect that the primary reaction of most listeners would be something like this: "Ah, I notice that the speaker has chosen the obscure word 'horsefeathers' in place of the canonical term 'bullshit' -- I wonder if the reason for this puzzling behavior is that he is personally uncomfortable with the word 'bullshit', and so I should remember to avoid its usage myself when in his company, or is it instead that he routinely acquiesces to the arbitrary nonsensical linguistic demands of a small minority?" Personally, I would prefer that listeners would be considering the idea that I have just expressed, rather then wasting time fretting about all this "dirty word" bullshit. I am therefore not particularly amenable to these contrived compromises.