Corrupt the Cutie: He agrees to feed people to Audrey II to keep it alive and win Audrey's affections. However, after he feeds Audrey and realizes what Audrey II is planning, he decides to try destroying it. He fails in the plays, but succeeds in the movie.
Defeat by Modesty: In both versions of the film, Audrey II thwarts Seymour's attempt to ax it by pantsing him, prompting Seymour to drop the ax and duck behind a counter.
Karma Houdini: Seymour killed two people (he let Orin die despite making it clear that he could have helped him and he backed Mushnik into the plant) and considered going even further (he signed the contracts in "The Meek Shall Inherit", implicitly agreeing to kill others in the future. This is made clearer in the play where the song is extended, but the actions remain the same in the film.) but in the theatrical cut, he gets away with absolutely no punishment whatsoever-Audrey likely never even learns that he is a murderer.
It can be argued that Seymour finally standing up to and destroying the plant thus preventing the destruction of the human race pretty much makes up for the world being less one sadistic dentist (which WASN'T his fault, despite intentions to the contrary) and one greedy, albeit somewhat kind, shopkeep (which may not have been entirely on purpose whatever the plant said). Both deaths are made a lot more ambiguous in the film than the play, and can be interpreted as due to Seymour's actions or not.
The Director's Cut makes it pretty clear that he didn't get away with anything, even if you don't count his death. Orin and Mushnik died only because Seymour doesn't prevent their deaths, and they both would have harmed him (Orin with dental sadism, Mushnik through blackmail) even if he had saved them. Audrey, on the other hand, he consciously fed to the plant, even if it was at her own selfless request. If he hadn't done it, Audrey II might not have been strong enough to tear down the building and eat Seymour whole.
My God, What Have I Done?: The film gradually leads Seymour to this. He's horrified that he chopped up Scrivello and he led his boss into Audrey II's jaws. Eventually, he realizes that he's gone too far and doesn't want to continue with what he's been doing.
Enfante Terrible/Creepy Child: "When I was young and just a bad little kid, my Momma noticed funny things I did, like shooting puppies with a BB gun, I'd poison guppies and when I was done, I'd find a pussy cat and bash it's head, that's when my Momma said..."
Pet the Dog: When he first meets Seymour, he bullies him a bit, however in two instances he was nice to him in his own depraved way. Before knowing who he is, he offers him some Nitrous Oxide, something he doesn't even give his patients. When he does know him he acts starstruck and is genuinely amazed that Seymour was able to have a plant as big as Audrey 2.
Played By: Tichina Arnold, Michelle Weeks, and Tisha Campbell-Martin
Greek Chorus: An interesting example, going back and forth between standing outside the action and commenting on it to the audience, and interacting with the other cast members using no special out-of-character knowledge. You can keep track by the costumes; when they're characters the girls wear worn-down clothing appropriate to residents of Skid Row, and when they're a Greek Chorus they've changed into sparkly dresses.
Expy: Of Wilbur Force, a masochistic dental patient Jack Nicholson portrayed in the 1960 movie.
Jerk with a Heart of Gold: While he is a Masochist, he understands not everyone is as enthusiastic to pain as he is. And since he opted for the most painful procedure on himself, he honestly considers the poor kid with the wired jaw to be considered lucky.