RE: Sometimes it's Good to be Angry
It's an interesting topic. What I have learned from the spiritual sciences is that this type of intention around competition will produce negative karma. Healthy competition, in other words, playing the game without manipulation, for the sake of the game and to improve your performance, produces "good" karma.
If someone is trying to rip you off, it is appropriate to be angry, there is no negative karma produced. But in the case above and when the intention is to do harm, then negative karma will weigh on the soul, producing tension and dullness.
I've learned a valuable trick. When you have negative thoughts about someone or something, throw it back to the Universe. Tell the Universe to take the thoughts away from you and you will feel it dissolve, your soul will be lighter for it. Try it.
I agree that experiencing the "negative" emotions over a long period of time can be harmful, stressful, etc. Having said that, the concept I am suggesting is that anger, hate, resentment, lust, vengefulness... some of these emotions have ironically extracted the best out of people. For instance, take a look at art - the tortured artist (Van Gogh), the self hating rockstar (Kurt Kubain), the alien junkie (David Bowie)... Suffering and pain creates beauty too, oftentimes more so than feeling happy and grateful.
Sure, it comes at a cost as the person is living in a constant chemical storm, but hey, for every action in life there is a reaction.
For times when I will be of need to ease the negativity off my soul I will try out your trick, thanks for that. :-)