I'm going to really shout at a manager of a repair shop
Why does he deserve to be shouted at?
Because he hasn't fixed my car yet. What is going on?!
Don't let your anger get the better of you. You should be polite to the manager in public. He might ruin your car because of it.
I'm not fucking kidding around. My car has been broken for a week!
I get that you are upset, but you should try to be polite to the manager. Screaming about your car is not going to get it fixed any faster.