Have you ever got angry whilst riding, jabbed your horse in the mouth, shouted at your horse, perhaps booted it in the ribs!
“Remember this … “You are not a good enough rider to be chastising your horse that way!”
Whatever your horse is doing, it is because he is receiving your signals and responding to them, or because he does not understand yet what you want. It is not wilful defiance on the horse’s part and if you are angry, you clearly don’t understand this. If you don’t yet understand this you have a long way to go.
There is no place for anger in Dressage!