Who is at fault if you are pulling out of parking space and hit the rear bumper of a car not parked straight on the right side with your front bumper?

More than likely, both parties. If there is enough damage to make a claim then it would be up to the insurance companies to make a decision. The claims would more than likely cancel each other out. If the other car is not moving and you are moving, there is no question that it will be ruled to be your fault.