Taboo

A taboo was an element of a society's social etiquette. They were laws, rules, traditions, ukuzila, etc. These taboos were implicit rules that formed parts of societies or groups, which its peoples followed or were constrained by. (PROSE: The Also People)

Cultural taboos

The Third Doctor remarked to the Marine Space Corps and to Sarah Jane Smith that 'the more primitive the society, the more complex the taboos' with regard to Sarah's transgressing the Great City of the Exxilons and interrupted sacrifice on Exxilon. (PROSE: Death to the Daleks)

The Master was called out by John Benton for referring to sergeants as "my dear fellow", causing the Master to remark on the 'tribal taboos of army etiquette'. (TV: The Time Monster)

On Sentarion all religious matters were utterly taboo. (PROSE: Shakedown)

Czhans had no taboos at all. (PROSE: Death and Diplomacy)

A node in the Library requested that visitors respect personal access codes regardless of species' hygiene taboos. (TV: Silence in the Library)

One account suggested that the extension of regeneration cycles was a taboo topic, and that the technology was developed during the Fifth Doctor's lifetime by the renegade scientist Ophiuchus. (COMIC: Ophiuchus)

A lot of Faction Paradox's actions and interactions with the Great Houses was a reaction or challenging their taboos around time travel and their related ideologies and practices. (PROSE: Alien Bodies, Unnatural History, The Book of the War)

Physical taboos

On Gallifrey physical violence was considered taboo. (PROSE: Doctor Who and the Invasion of Time)

Since Pythia's curse Gallifrey had for some time a taboo concerning physical intimacy, and especially pregnancy. (PROSE: The Book of the War)

Sexual assault was considered a major taboo by the Sorvix. (AUDIO: Tagged)

Nudity

In 1941 Bernice Summerfield observed that the Germans had a culture with a nudity taboo. (PROSE: Just War)

In 1958 Chris Cwej mused that people were still incredibly sexually repressed in the Western nations in the mid-20th century, with nudity being a taboo during this period. (PROSE: Bad Therapy)

Trakenites had similar taboos to Earth circa 20th century regarding the display of genitalia. (PROSE: Cold Fusion)