Elsa breaks down crying after Jojo reads the blatantly made-up breakup letter from her fiancé. Jojo interprets this as her believing his lies, but it's later revealed that her fiancé is already dead, so Jojo's false letter instead reminded her that she will, in fact, never see him again.
The more indoctrinated Jojo is into Nazism, the more the imaginary Hitler is Adolf Hitlarious, but the more that Jojo begins to question Nazism, the more Hitler becomes less friendly. The more Jojo views Jews as people and not the monsters of Nazi propaganda, the more Hitler's racism and antisemitism become monstrous and horrifying. Hitler reduced to a pathetic little maniac begging for a "Heil" reflects Jojo, and by extension Germany's, final disillusionment with Nazism.
Hitler keeps trying to give Jojo cigarettes. To a kid like Jojo, smoking is just an "adult" thing to do. It also shows how little Jojo knows about the real Adolf Hitler, who was famously averse to tobacco.
Jojo's facial scarring after his accident with the grenade apparently making him hideous and possibly frightening other children if he went back to school seems to be an Informed Deformity. It really isn't that bad, even just after he leaves the hospital. The reactions only make sense when it's remembered that this is in Nazi Germany, where Nazi ideology would indeed treat slight disfigurements or any aberration from the Aryan ideal with disgust.
Yorki stating that his uniform is not paper, but a paper-like material developed by German scientists. This is a silly reference to an actual practice in Germany, as shortages of certain materials developed during both World Wars. Ersatz (German for 'substitute' or 'replacement') products included ersatz coffee, ersatz rubber, and ersatz sausage, and yes, that's where the trope name came from.
Fridge Horror
The realization that Klenzendorf abruptly showed up at Jojo's house during the Gestapo raid because he witnessed Rosie's execution (or at least the events leading up to it). He immediately ran over to protect Jojo (and by extension Elsa). Note that he tells Jojo to not go out as he leaves: he doesn't want Jojo to see his mother's hanging body.
Were the Russians seriously going to execute Jojo, a ten-year-old boy, via firing squad with all the other Nazi war criminals if Captain K hadn’t intervened? In fact, they probably were. The Soviets were not known for their light-handed treatment of Germany at the end of the war, committing a staggering amount of war crimes and persecutions against German civilians.
