I don't understand the difference between Jehovah's Witnesses and Christians?

I know there's a difference and that Jehovah's Witnesses are much more annoying, for Christians at least don't hunt you down and knock on your door, but I don't get it? JW's always say there's no difference, but it's like Christianity and Catholicism, there's a difference, or it'd be called the same thing and it's a tiny little difference. What's the difference?