Not a happy bunny
A British expression that means a person so described is decidedly unhappy or annoyed about something. It is first attested from the late 1980s/early 1990s and it is not known who coined it or for what reason the word ‘bunny’ (a pet name for a rabbit) should be used in the expression. The expression almost always appears in the negative and there are very few instances where a person is described as ‘a happy bunny’. See also Happy Camper.