In my opinion the worst commander has go to be Commander Geoffrey Basil Simpson-Simpson. He is famous for his amazing victory on Lake Tanganyika in WW1, the only British Naval expedition in Africa during the war. Now your probably wondering, how could a person who won a victory be an awful commander? Let me explain.
During the war he was put in control of two cruisers I think it was. He decided to take out an enemy submarine by hanging wire between the two ships and then taking out it's periscope. What he did was take out a submarine......but one of the British ones. He was then put in command of a group of gunboats. He then docked them in harbour and went to make love to his wife making sure they were somewhere he could see them. he did see them, he saw them get struck by a German torpedo and he saw them sink. Even his victory on Lake Tanganyika was down to luck. He took out three heavily armed ships because they didn't know he was there and they were able to knock them out by surprise and use captured ships to fight as well. But he wasn't even commanding the assaults when they happened, the victories were made by his second in commands. He was rude, frankly and idiot and wore a skirt while in Africa. In fact, he was so awful he was given the easiest office work in the navy and he was only chosen for the expedition because all other commanders were busy blockading the Germans and the navy really didn't care about the situation in Africa. To me, he is the worst commander ever in history.