Claire is an example of Sir Not-Appearing-in-This-Trailer, as are the characters connected to the Daily Days. Why? Reporters don't report on themselves, and the series is through the lens of that paper's reporting on the Flying Pussyfoot incident.
The eventual reveal of why Jacuzzi, the most timid character in the whole series would have the most attention-drawing feature, his huge jagged sword tattoo. It seems especially incongruous when you see that the tattoo is being used to identify him on his wanted posters. Turns out it's a CMOH: Jacuzzi got it after his best friend and later girlfriend Nice scarred herself horribly after an explosives accident, so they could match and she wouldn't be alone in being stared at.
In the novels, the reason is different. The reason he gets a tattoo is because Nice's eyesight became very damaged by the accident, so he got it so that she could always recognize him no matter what.
Isaac and Miria hatch a rather odd plot to steal an entire museum. It doesn't quite work out, so they just steal the door to "keep people from entering." Crazy? Maybe, until you realize that with the door stolen, the police would close the museum down for an investigation. So their plan WORKED, but maybe just not in the way they intended.
Also notable is that Isaac and Miria performed the post-episode trailers as if they were actually watching the show and guessing what would be in the next episode. Take into account that they're immortals living within the Naritaverse, where Baccano is actually a television show by the time the events of the Durarara!! anime start (Baccano plays on the big screen TV in the middle of town in some shots). Isaac and Miria could very well have been watching themselves on television in-universe without actually breaking the Fourth Wall at all; just talking to each other about the episodes.
One of the points brought up against Czeslaw is the time he abandoned Mary in the closet on the train. What occurred to this troper when discussing it with a friend was that though he abandoned her, he apparently went out of the way to take her to an empty, secluded area of the train when he could have ditched her the minute they were out of her mother's sight. Hiding her in the closet was a good idea, because if Mary hadn't accidentally made noise, she most likely would have been safe there. After all, who would think to go far back into the train and check the closets for people hiding? It was her knocking over cleaning equipment that caught the attacker's attention and put her in danger. This might be supported by the fact that even eighty years later, he still remembers the time he spent with her fondly. Czeslaw was trying to keep her safe, even if he didn't realize it!
When you only follow the anime, it seems strange that later on Claire introduces himself as formerly being Claire Stanfield and is no longer a conductor, until remembering that Dune of the Russo Family had red hair, was close to Claire's height, stole a conductor's uniform earlier and had his face completely smashed beyond recognition. Turns out the police pronounced Claire dead because Dune fit the description best.
The unnamed narrator in the first book has a moment of this when he thinks a little too hard about Firo and Ennis's relationship and realizes that, since Ennis was a part of Szilard and Szilard is now a part of Firo via Cannibalism Superpower, Firo can technically be seen as screwing himself. He wisely decides not to voice this thought in front of Firo.
When you realize that thanks to his immortality, Dallas is continually drowning to death in the opening.
The interactions between Czes and Fermet are already horrifying, but take a look at this screenshot◊. Judging from the camera angle and Fermet and Czeslaw's respective positions, Fermet could only accomplish this by sitting directly on top of Czeslaw's chest. And Czeslaw shows no reaction to this, which implies that Fermet positions himself like that a lot (or at least, enough for Czes to be used to it). There's something really disturbing about how intimate Fermet likes to get with Czes, and it gives a whole new perspective on some of the things Czes says to people when he feels threatened...
Before being saved by Chane, young Mary was being attacked by a goon who specifically talks about how he only enjoys preying on those weaker than him, with some comments that seem to imply a sexual nature to his attack.
Ladd Russo once claimed that he was physically weaker than Jack Dempsey, a statement which Word of God confirmed to be the truth. Anyone who has read the novels knows that Ladd is freakishly strong, capable of punching through a reinforced steel door. Baccano!'s Jack Dempsey must be a fucking nightmare!
On top of that, a real-life Dempsey was accosted by a mugger in 1971. God knows what would happen to that mugger if he went up against Baccano!'s Dempsey.