Shit

In a parallel universe, a Time Lord chided a colleague for his language when he reacted to news of the Doctor's escape with the exclamation "Oh, shit!" (AUDIO: Exile)

Cousin Eliza mentioned that the lions in Trafalgar Square "gave [her] the shits." (AUDIO: The Shadow Play)

In a fit of rage, Ianto Jones once lamented, "Like you care. I clean up your shit, no questions asked, and that's the way you like it." (TV: Cyberwoman)

Gwen Cooper used the word when she discovered that she needed all of Torchwood Three's members eye prints in order to open the Rift. (TV: End of Days) She also used it to describe a piece of modern art as shit. (AUDIO: More Than This)

Kaitlin Russell once exclaimed, "Holy shit," after she and Rhys Williams found a body crushed under plastic. (AUDIO: Sargasso)

Rex Matheson's usage
Rex Matheson told Jack Harkness that he said "some crazy shit" when he spoke about his newfound mortality. (TV: The New World) He said "bullshit" after returning to the US from Heathrow Airport (TV: Rendition) and after Brian Friedkin set him up. He referred to Torchwood's gathered information on PhiCorp "this PhiCorp shit" and said "oh, shit" when Vera Juarez told him that Jilly Kitzinger was returning to her office, where Gwen Cooper was. (TV: Dead of Night)

Rex asked Vera about "this Dead is Dead shit" and told his father that his claims that he had never cared for anybody but himself were "bullshit". He said "shit" when climbing the stairs of the PhiCorp building and after shooting the Gentleman and referred to Jack's talk of his past as "that shit". (TV: Escape to LA) He said "shit" when a nurse checked that he was breathing and had a pulse and "holy shit" when he saw Vera in a module. (TV: The Categories of Life)

He said "shit" when he spotted Allen Shapiro arriving at Angelo Colasanto's house and "holy shit" at seeing the effect of the null field generator. (TV: End of the Road) He said "shit" when he mentioned Charlotte Wills's partner, forgetting that she had left Charlotte. He said that The Devil Within was full of "blood and Satan and that kind of shit" and said "shit" when Charlotte told him that John Podesta's blood was not on file and when Esther Drummond asked for translation. He told Esther not to start with "that hugging shit". (TV: The Gathering)

He said that he had seen "some crazy shit" with Torchwood, said "oh, shit" when Esther joined him in going to the Blessing, said "this shit hurts" when the Blessing was attracting Jack's blood within him and said "shit" when he learnt that Charlotte Wills had been the mole in the department. (TV: The Blood Line)

Behind the scenes
In COMIC: Assimilation², Jean-Luc Picard and Worf use French and Klingon equivalents of the word "shit", "merde" and "qi'yah" respectively.