Response to failing to do the one and only thing you had to do. This is told, either in a disgusted, mocking, or angry tone to people, animals, inanimate objects, and anything else that fails to complete the simple task for which it was designed.
A way to express total fail, epic fail, especially when the one job was very simple.
To a cheap park bench that broke while I was sitting on it, "You had one job, park bench!"
To an accountant who was fired for inaccurate computing of business records. "You are supposed to be an accountant, right? You had one job, Sandy."
To a friend about my broken down car, "Damnit, it had one job!"