So apparently the new doctor likes to swear. So much, that the crew had to beg him not to add swear words to his dialogue.
“Does anyone have any idea what actors do for a living?” asks the exasperated thespian Lloyd Woolf, rhetorically. He jokily imagines what the production staff had to go through when they worked with Capaldi onThe Thick of It. “We begged him to stop swearing — begged him — but he just slurred something about an adult audience and carried on…”
As for the Doctor Who team, he reckons that, if they saw what The Guardian had to say, they will be feeling “very relieved that Peter has accepted that he’s on a family show and has agreed to stop adding creative swears to his dialogue”. - Source
Here's a neat little fan video on Peter Capaldi's swearing.