Use the adjective garish to describe something that is overly vivid, bright, showy, and in bad taste — like the DJ's garish outfit that is a flashback to the disco era.
Garish comes to English from the Old Norse word gaurr, meaning "rough fellow." It is often used to describe colors, clothing, decorations, and other things that can be elegant and tasteful. Because the word connotes bad taste, however, it is rarely used in a complimentary way. If you say to your friend, "I like your garish hair and makeup," she is not likely to take it well, unless, of course, you are going to a 70s flashback party.