(n.) the awkward or pretentious use of foreign words in everyday conversation
Dropping foreign words into everyday conversation so as to appear sophisticated is called cacozelia.
Cacozelia is an example of a rhetorical vice—a turn of phrase or similar linguistic phenomenon recognized in the work of untalented or inexperienced speakers and writers, and so best avoided in all good prose or oratory. Although the definition we gave on Twitter is the more usual, sometimes cacozelia is used more loosely to refer to any stylistically affected or overwrought language.
(Incidentally, the vice of using a mixture of clashing languages in quick succession—as in “dismissing the hoi polloi is de rigueur these days!”—or the unintentional misuse of foreign words or expressions—“mangetout, Rodney, mangetout!”—is called soraismus.)
The word cacozelia itself essentially means ‘poor imitation’—likely in the sense that someone guilty of it isn’t exactly succeeding in imitating a learned or fluent speaker. The ‘caco–’ here is the same Greek root as in words like cacophony and cacosomnia, while the ‘–zelia’ is an etymological cousin of zealousy, and derives from a Greek root, zelos, meaning ‘emulation’ or ‘rivalry.’ Et voilà. Le mot juste.