Getting pissed off on the mat makes my aikido worse every time. Now if someone aggravates me I stop training with them. Not just because I don't want to face the challenge, but the opposite. I want to go all the way. And it's just not worth the pain to me anymore.
I train to learn control. If I am truly in danger of losing control, I will step off the mat. When I know I can maintain control I learn immensely in the situations where I am being frustrated and angered. Sometimes slowly, sometimes not.
It is handy, however, to train with seniors who are knowledgeable enough to read the signs and to take responsibility for that as well.
There is no doubt in my mind that good decision making can result from anger and frustration tempered by a relaxed and analytic mind. When anger spills over into rage is when the tool (anger) becomes misused.
People struggle for mushin and to remove anger and fear and perhaps even passion from their decisions and actions. This is admirable, but I think, not the point. I'd much rather achieve a level of mushin that allows me to let anger, fear, and passion to exist in me, but to flow through me and power my actions appropriately.
I don't have any interest in becoming passionless, merely unaffected in a negative way by my passions. Even that is a silly desire because one day I will lose those I love to circumstances and what I feel will certainly be negative; however I wouldn't give up the emotional connection offered to avoid such negative experiences. Why would anyone?