I'm going to tell my flatmate to f off because she wouldn't follow the rules we had set together
What were the agreed upon rules?
We agreed to not keep the dishes in the sink without washing them. Yet she is not keeping her promise.
You should keep harmony with people you have to live with. If you yell you might create a bad mood in the home and make life unpleasant for everyone.
Nah I can't stand this. I'm going to get up and yell.
I understand that you are angry, because your roommate should have been honoring your agreement.  However, now is not the time to act on this, because you are a bit too wound up, and it could cause problems.  Let things calm down, and then discuss the problem, perhaps you could do the dishes once per day, and she will take on another shared chore all by herself.