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How to avoid fighting on christmas
Identify your own triggers in advance.
You know yourself better than anyone; you also know which family members have the ability to set you off. Often it's a case of like versus like, in which you choose to pick on the other person because they personify something you don't like about yourself.
This is unhelpful and certainly only serves to make the other person feel defensive. If you know what sets you off, you can remind yourself that it's your feelings getting worked up and that you have control over how to respond.