I despise excuses. If I have set a task for a servant, I have done so based on many factors including training goals and information the servant has provided for me regarding their responsibilities and limitations. I therefore expect the task to be completed.
What I do not expect, nor will I tolerate, are excuses or rude behavior. Telling me you are "using your safe word" to get out of doing the tasks I set for you is unacceptable. Especially if I know you have wasted time at your computer earlier in your day.
I will not demand any service I do not believe you are capable of completing. I will not require service which will keep you from doing your job or would interfere with your family. I will punish you for failure to do what I have told you to do. If you wish to be released, fight me on this issue. It is one of a very few ways to quickly find yourself released from my service.