I understand and basically agree with the posts above regarding "toxic" people and distancing yourself. However, events may occur that make this impossible or difficult (dealing with family executors for example).
I've come to realize that it is similar to dealing with any unstable person - avoid as much as possible and NEVER argue or try to persuade with reason and logic - because that's a waste of time. When I have to interact with this type of person among my relatives I use an "accommodating" stance, agreeing and MAJOR ego-stroking of the other party. Often, this type of personality stems from low self-esteem which results in jealousy and then antagonism. (Wow-talk about donning a therapist-pose! - sounds good though

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I may appear to have it much more in control than I actually have had in the past - I basically moved 3000 miles away to escape .....