I have posted a note on Administrator ItsZippy's talk page asking for help with a disruptive editor. I realized yesterday that Mrm7171 meets the criterion in that he is intimidating other editors, making them reluctant to contribute to the article because he/she will undo their work, and then engage in a long aggressive argument that generates walls and walls of text on the talk page, yet fails to accomplish anything productive. It has taken me four months to add 4-5 sentences, and each one was a protracted battle with this one editor. I have had no problems with any other editor, even when we had different apparent backgrounds and perspectives.