Lists by aebars
Dieselpunk, as opposed to steampunk, encompasses science-fiction, fantasy and action-adventure set in the 1920s through 1950s - or at least works based on the aesthetics thereof. If many people would use the words "pulp, "retro" and/or "deco" to describe a work of fiction, then it's probably dieselpunk.
A character (or characters) starts out (comparatively) sane, sensible and rational. As the film goes on, however, they degenerate into hallucinatory, homicidal, schizophrenic insanity. Inform me of more, by all means.
(Films where the insane character starts out insane, such as 'Psycho' or 'Silence of the Lambs', do not count. To qualify, a film has to show the progression from sane to insane.)
If you're cynical, you can regard this as "Become a Chick-Flick Expert in 250 Easy Steps." Suit yourself.