Here's a problem - when you're dealing with a toxic person, especially when managing a toxic person, there is the illusion that some coaching will change things and we can get on with life. Unless the toxic person is off the charts, most of these people have some very good skills that we'd kind of like to keep. So we'll send them to a conflict resolution class and move on. The problem is that these people may require way, way more energy that we think.
Like Seth says, there are too many people who are way easier to work with. Go work with them.