what happens when i block someone that is not following me on twitter?

[Jack]

Even if you block someone, they can still see your tweets, as your tweets are public unless you change your privacy settings. If you block someone, they will not be able to follow you, or you follow them. They are still able to tweet you as, unlike facebook, they do not have to write on a wall, they just have to write an @ name, but you shouldn't be getting any notifications of them tweeting you. Hope this helps!