It's implied Orin is a sadist and into S&M. No acts are shown but implied through actions and dialogue. Such as Audrey's arm in a cast from being "handcuffed"
A man-eating plant eats several cast members. Songs involving the plant often make references to blood and killing.
In each of Orin's scenes, his sadistic nature is played comically, but can be disturbing to some viewers. Orin commits many comically violent acts during the song "Dentist!". In it, he makes references to injuring animals including bashing a cat's head, he hits a nurse in the face twice, knees a teenage patient in the groin, and jams dental instruments into patients' mouths to cause pain.
Seymour holds Orin at gunpoint in one scene.
Seymour chops up a body in an alley and feeds it to the plant who eats it eagerly.