To qualify as one in my book you have to be a serious problem: one came to give me a beating at work and the only way I got away was to find a corner and a weapon until he got distracted.
Another one made life at work so frustrating for two years that I left one of my best jobs ever just to never have to deal with that guy alone.
Unless someone here is stalking you, messing up you life etc then try something like this instead: there are a lot of people on HN who disagrees with me in ways I didn't expect.