I understand.. In my case it's my dad that's like this, has sudden reactions. It's always about emotion. I think it's hopeless that he would change and realise his behaviours. So I've just completely given up on getting angry and just let him have his tantrums.. I always talk to him smoothly and quietly. I let him know what I think. He always goes back to normal afterwards and accepts what I've said (so in a way I also feel like his tantrums are just emotions he wants to express and let out, but not really directing them towards anyone in particular).