bunny boiler
According to Wikipedia, a "bunny boiler" is "an obsessive and dangerous individual, most commonly referring to a jilted lover who is stalking the person who has spurned her or him. [...] The phrase derives from a famous scene in the 1987 film Fatal Attraction where a scorned woman [...] boils [her ex-lover's] daughter's pet rabbit in a pot."
Yikes.
See also Phrase Finder's entry, which suggests that the term came into popular and widespread use in 1994. Which makes me even more surprised that (I'm pretty sure) I've never encountered it before.