A slang expression from the US Army, it
originated during the Vietnam War and may be derived from the
Vietnamese “di di mau", meaning to go quickly. Usage by American troops altered the meaning somewhat so that it referred to walking with dance steps or with an
exaggerated swagger. It was used in the context of walking carelessly whilst on patrol in enemy territory, without paying proper attention to your surroundings and putting yourself and other members of the patrol at risk. The meaning later expanded to include moving or acting without considering other people.