This is a kid type of thing that Im pretty distant from. Still when talking with my brother on the phone its funny to hear the background antics. Why are you mad? Whats gotten you so mad?
You're allowed to have emotions, and as a kid they're hard to mask or deal with. So letting your kid feel them and modeling how to deal with them is the right way to let them learn, rather than telling them they can't be angry and just having them feel guilty for their "wrong" emotions.