Underpants were a type of clothing worn by humans and humanoid species.
Nyssa was captured by The Garm while wearing underpants. (TV: Terminus)
Rory Williams was interrupted by UNIT in the process of dressing and marched at gunpoint into the kitchen wearing underpants – he told the Eleventh Doctor, “there are soldiers all over my house, and I’m in my pants”. (TV: The Power of Three)
The Eighth Doctor wore question mark underpants. (COMIC: The Glorious Dead) When Osgood asked the Twelfth Doctor why he stopped wearing question marks, he told her that he too wore question mark underpants. (TV: The Zygon Invasion)