Note to self: when expected to enter a situation that can evoke strong emotions, plan what to do and what to say in advance, before emotions start interfering with ability to think, rehearse the plan in your mind, and only then allow the exposure. Next time I notice that I started to argue with emotions rising up, I cut myself short and regroup.

Addition a year later: I'm currently doing a study group with a friend based on a book called 'Crucial Conversations', which is entirely about being more effective at communicating in emotion-laden situations. Highly recommended.