Demob suit

[Becky]

at the end of the Second World War, returning servicemen underwent a demobilisation process at various [centres] around the country. As part of this process of [transitioning] back into [civilian life], they were issued with an outfit of civilian clothing. This included a new suit, which became known as a demob (short for demobilisation) suit. Accordingly, the phrase has become synonymous with any suit that looks sufficiently mass-produced and out of style that no-one in their right mind would buy it themselves.