Cannibalism

Cannibalism was the act of eating members of one's own species. While this was sometimes a choice or a lifestyle, for some species this was a natural activity. Mayflies practised sibling cannibalism, leaving only the strongest of them left in the end. (TV: Reset)

Cannibalism was a cultural practice of the Valethske, ordinarily as a form of execution, but occasionally occurred during feeding frenzies. (PROSE: Superior Beings)

The Brynblaidd cannibals killed and ate wanderers near their village every ten years. (TV: Countrycide)

At some point in Tennessee, there was a case of cannibalism, though the culprit claimed not to remember the crimes. (PROSE: The Juror's Story)

Alan Jackson at first thought the Slitheen were cannibals when he saw their skin suits lying around. (TV: The Lost Boy)

Mother Nothing was a cannibal who resorted to consuming her entire race, including her hatchlings, when her home planet was struck by a great famine. (AUDIO: One Enchanted Evening)

According to the Second Doctor's recollection, humans in the Far Indies ate their own kind. He and Shockeye also assumed that shepherd's pie was made from a shepherd. (TV: The Two Doctors)

Behind the scenes
In the real world, the meat in shepherd's pie is not made from actual shepherds.