It's best not to get angry when you play, period. And if you want to be a professional table tennis player, you better learn to control your emotions. (Even John McEnroe had his best tennis matches when he wasn't throwing fits.) However, if you do get angry sometimes in matches, then you should at least learn to channel your inner "rage."
Ever get really mad about something, to the point that you couldn't think straight? That is "Hot Anger." It's pointless and should always be avoided. And yet that's what often happens in competitive matches, where a player gets angry either at himself, his opponent, the playing conditions, the tournament director or referee, or anything else. The result is poor focus, poor execution, and poor play.
On the other hand, sometimes these anger issues can benefit you, if you know how to take advantage of them. If there's something that angers you, don't get "hot angry," get "cold angry." The difference is now you are thinking with ice-cold clarity with a single purpose in mind - overcome whatever it is you are angry at and beat your opponent. With "cold anger," you become single-mindedly focused and determined.
Some top athletes truly thrive on this, even going out of their way to find slights against them to give them incentive to push themselves to the limit - but they do so with "cold anger." If a team is predicted to do poorly by the experts, players can use this as incentive with "cold anger" - but if they truly get angry at this, with "hot anger," then they will likely self-implode - and that often happens. So next time you feel "hot anger" coming on, change it over to "cold anger" and use it to your advantage.