Interjection used to express displeasure when something doesn't come out the way you wish
Silly girlfriend:So are you taking me out for dinner tonight?
You:Sorry hunny,i can't.I'm going to watch the football game with the guys.
It's a metaphor used to designate that some obsessive maniac loser is stalking you.
Person A:OMG!That weirdo we met the other day has been insistantly ringing me every single day and also sending me all these emails asking me to go out with him.
Person B:Oh geez!He's so gonna boil your bunny.