"La donna è mobile" was a song which the Doctor sang in his third incarnation whilst driving to the Inferno drilling project on Bessie (TV: Inferno) and sang it again during his eleventh incarnation whilst taking a shower. (TV: The Lodger) In Antarctica, Tito sang it while lying on his bunk. (TV: The Tenth Planet)
Behind the scenes
The piece is never named in DWU fiction, but it's unmistakably rendered. It is a canzone from the opera Rigoletto, and the title means 'Woman Is Fickle' in Italian.