Bunny Boiler is a pejorative term for an obsessive and dangerous individual, referring to a former lover who stalks the person who spurned them. The term is normally used for a woman.
From the 1987 film Fatal Attraction, written by James Dearden and Nicholas Meyer. The plot concerns a woman scorned, Alex Forrest - played by Glenn Close, who obsessively pursues her ex-lover, Dan Gallagher - played by Michael Douglas. The phrase comes from the plot device where Forrest boils Gallagher's daughter's pet rabbit.
Gallacher's suspicions should have become aroused at Forrest's line when trying to persuade him to meet her - "Bring the dog, I love animals... I'm a great cook."
The bunny boiler phrase, taking the lead from the film, was first used to refer to someone who is unable to remain rational at the end of a romantic relationship. Very quickly that became moderated and used, with some degree of irony, in much less extreme situations. Any needy, mildly possessive or even just annoying woman is now liable to be described as a 'bunny boiler'.
