Rabbits!

"Rabbits!" was a negative exclamation favoured by Tegan Jovanka. She used it to indicate displeasure or frustration at an event. (TV: Logopolis, Frontios; PROSE: Graham Dilley Saves the World, PROSE: The Assassin's Story)

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.