Rabbits!

"Rabbits!" was a negative exclamation favoured by Tegan Jovanka. She frequently used it to indicate displeasure or frustration at an event. (TV: Logopolis, Frontios; PROSE: Graham Dilley Saves the World, The Assassin's Story; AUDIO: Psychodrome, The Star Men, Aquitaine, The Peterloo Massacre, The Emerald Tiger, Eldrad Must Die!, The Entropy Plague)

Behind the scenes
The exclamation does not seem to particularly be popular, real world slang. It may have simply been a Janet Fielding-ism or an invention of the writers.

On an interview for Doctor Who Magazine 431, Janet explained: "Well, [Tegan] was hardly going to say, 'F*** off and die,' was she? Not on BBC1!"".