Dieselpunk is an art style and subculture that blends the aesthetics / pop culture of the 1920s - 1950s with today. To dieselpunks, the "diesel era" was a time defined by warfare, Art Deco, pulp heroes, swing music, and noir gum shoes.
Its akind of like steampunk, except with internal combustion, because steampunk wasn't dirty enough.
Me and John saw a group of cosplayers in a steampunk show that didn't look victorian at all. They wore fedoras, goggles, ww2 gear and retro-futurist tech, but from a different timeline. Turns out they were dieselpunks