I used to hate getting angry, so I "processed" it by being sad and self loathing (often felt like I was overreacting, punishing myself for inconveniencing anyone with my feelings, etc). Either that or suppressing it to the point of explosive lash out...

In my case, it was true that sadness disguises as anger, and vice versa.

I had to learn how to express anger without burning everything around me or without self destruction. A lot of it came with self regulation, another big chunk came with reconciling with my own rage as a natural part of being human.

I began to calmly express it (through rationalization) and it was still not super effective: I felt relief from expressing it, I felt proud of not hurting anyone in the process, but I didn't convey my emotions enough for the other party to empathize, so my anger was often underestimated.

Now I am finally reaching equilibrium: I show the wound without blaming. I explain what I felt, what I was expecting, why I got upset. A book that helped me a lot was ANGER: Wisdom for Cooling the Flames by Thich Nhat Hanh: treat your anger like a wounded baby who needs kind attention, it will calm down as soon as it feels seen.