If anyone ever says that you walk on mephitic clouds, be ready to defend yourself — or be embarrassed. Mephitis is a harmful, bad-smelling vapor from the earth — for example, the odor from decomposing organic matter or poisonous gas from a mine. It can also refer to just a plain ol' stench or bad smell. In George Bernard Shaw's Man and Superman, Don Juan expounds on romantic illusion: The great central purpose of breeding the race ... that purpose which is now hidden in a mephitic cloud of love and romance and prudery and fastidiousness, will break through into clear sunlight as a purpose no longer to be confused with the gratification of personal fancies ...