Thong

Historians who had been allowed access to the "Monster Vaults" of the databanks in the Doctor's TARDIS observed that the Abzorbaloffs of Clom naturally wore little more than a thong, as the drawing of sustenance through their skin required them to be as naked as possible. (PROSE: The Monster Vault)

The Eleventh Doctor refused to wear a thong, again, for his date with River Song on Temple Beach. (PROSE: A Gamble with Time)