At what point does it go from being a lawyer and using it wisely to being a bully and harassing people?

Separately: What penalties can be enacted to stop someone wasting the courts time? I presume you can't stop someone suing even if they have a history of it and even if people don't like the reasoning behind it. I assume a person could make claims like he is and lose a hundred of them and still sue the 101st. So what protections are in place to others ?