You do something inefficiently when you use more time, money, or energy than you need. The job may still get finished; it just costs too much along the way. He packed inefficiently, so the suitcase would not close. The company was run inefficiently for years. Same idea as inefficiency, but here you are describing how someone works, not naming the waste as a thing. It is at home in work talk, school talk, and everyday complaint. It is not a rude word, but it does judge the method.