Swearing
Swearing was the use of speech considered rude.
The Ninth Doctor once mentioned that the TARDIS' translation circuit had a swear filter that prevented the passengers from hearing any swear words; even an angry cavewoman's rants were translated as her saying, "Blinking", rather than a more apt phrase. (PROSE: Only Human)
The Malmooth Chantho respectively began and ended her sentences with "chan" and "tho"; as she explained to Martha Jones, to not do so would be akin to swearing. (TV: Utopia)
Yasmin Kahn's grandfather often swore loudly in Punjabi when he accidentally injured himself. He hoped that his young granddaughter hadn't understood, but she had. (AUDIO: Fallout)
The Twelfth Doctor's internalised anger sometimes lead to a preponderance of swear words appearing on the psychic paper. (TV: Dark Water)