This advice might seem counter intuitive but i've found that when i'm playing a 8-10 tables getting mad becomes less of a problem for a couple of reasons.

1. I Make more plays that I would consider "bad", but I don't spend time worrying about them because I have to many other things to consider. I am confident that I am a winning player so I try to keep myself playing as perfect as possible on all tables which means no overanalyzing past mistakes.

2. By playing many tables i don't get bored and try fancy plays that deviate from a tight aggressive style that is the easiest for me to profit with. By playing this type of style I give myself fewer chances to screw up the way I play my cards.

P.S. Playing many tables at once may in fact have the effect of magnifying your anger more so if this doesn't sound like something that will help you just ignore everything i've said.