In The Ten-Cent Plague, David Hajdu cites a statistic that, during World War II, no fewer than 50 comics featured Hitler on their covers (and I think that Hajdu's number is low--50 covers in a single year would be more likely). He references the cover to Thrilling Comics 41 (1944), which features the Commando Cubs (clearly a knockoff of Joe Simon and Jack Kirby's Boy Commandos) rading Hitler's bedroom (Hajdu 55). Here's the cover, courtesy of the Grand Comics Database:
The goal here, obviously, is to present Hitler (and Mussolini, who is hiding under the bed) in a humiliating light, and such humiliation would take even more bizarre and extreme forms in comics and elsewhere. During World War II, there was almost a subgenre of propaganda materials involving anal violations of Hitler, and it was considered acceptible even to include such images in children's entertainment, as this cover to Supersnipe Comics indicates.
The most well-known of these materials was probably the Hitler Pin Cushion, which can be seen here. There is also this one , as well as this one, which was advertised in a 1944 novelty catalog. Clearly, such an item was popular enough to spawn several different versions.
A gag along these lines is also used twice in the 1942 propaganda film The Devil with Hitler, produced by Hal Roach, about which you can find more here, including many stills from the film. In this slapstick comedy, the Board of Directors in Hell decide that they are going to replace the Devil--known here as "Gesatan"--with Hitler unless the Devil can convince Hitler to do one good deed before he dies. By the end of the film, Hitler, along with his Axis cohorts Benito and Suki Yaki, is trapped in a munitions room that catches fire. As Hitler tries to escape, a rocket flies up his ass and explodes, sending him to Hell. While Hitler is in Hell, demons proceed to stab his ass with their pitchforks, continuing the violation.
Several of the actors, including Bobby Watson as Hitler and Joe Devlin as Benito, returned in Roach's follow-up, Nazty Nuisance (1943). This film concludes with Hitler, Benito, and Suki Yaki all getting shot out of a submarine's torpedo tube and landing face down in the sand, with their butts in the air in a pose resembling the pin cushions.
Though he did play other roles, Bobby Watson had a successful career appearing as Hitler in at least 10 films, all the way into the 1960s. Most notably, he played the dictator in Hitler--Dead or Alive, a crazy 1943 film in which 3 mobsters are sent to Germany to assassinate Hitler. Also, both Watson and Joe Devlin teamed up again as Hitler and Mussolini in Preston Sturges's The Miracle of Morgan's Creek.