Pick a decade. Dress the part. Every look below was worn dead seriously by somebody who thought they had it figured out, which is the whole assignment. No costume shops required. Most of this is still in a closet somewhere.
Rock and roll on AM radio, soul 45s, surf guitar, and cars as the only real venue. Two camps ran the parking lot: greasers in leather and cuffs, and the clean-cut crowd in cardigans and saddle shoes.
Funk, soul, fusion, and the long instrumental break. Clubs got louder, hems got wider, and the horn section dressed better than the audience. Punk showed up late and cut the sleeves off.
Drum machines, boomboxes, and the first generation to dress like an album cover. Hip-hop made sportswear formalwear. Everything got a shoulder, a logo, and a can of hairspray.
Grunge, boom-bap, trip-hop, and mixtapes taped off the radio. The look was thrifted, oversized, and studiously uninterested, which took more effort than anyone admitted.