Alternative hypothesis: Your friends assume this is one of those cartoons-not-just-for-children that you talk about, and find it completely unfunny because it's a parody of something they haven't seen and don't care about.
I've been in the situation before of having a friend show me a "hilarious" parody of some computer game or whatever, and finding it completely pointless and unfunny, despite the friend loving it. And I'm pretty sure it's not because of some creationist-level bias, because I'm fine with good parodies of computer games I'm familiar with.
I've created this issue when attempting to show Excel Saga to non-anime-fans. It doesn't work if you're not familiar with the tropes it's laughing at.
My mother won't watch animated movies. It doesn't matter what the content is. Whether it's Sponge Bob or Grave of the Fireflies, she believes that animation is used only for shows for children, and that adults shouldn't watch shows for children. She's incapable of changing this belief, because even if I somehow convince her to sit and watch an animated film, she sees what she expects, not what's in front of her.
I think this is the same thing that creation scientists and climate-change deniers do. They literally cannot perceive what is in front of them, because they are already convinced they know what it is.
Here's an interesting test, which I discovered by accident: There's a hilarious series of fan-made parodies of My Little Pony: Friendship is Magic on YouTube called Friendship is Witchcraft. They took show videos and redubbed them to have different stories in which various ponies are robots, fascists, or cult members planning to awaken Cthulhu. I've shown these videos to four people without explanation, just saying "You've got to see this!" and bringing up "Cute From the Hip" on YouTube.
The same thing always happens. They watch with stony, I-must-be-polite-to-Phil faces, without laughing. Eventually I realize that they think they're watching an episode of My Little Pony. I explain that it's a parody, and they say, "Oh!" I'd think that lines like "I know we've taught you to laugh in the face of death," "If you think one of your friends is a robot, kids, report them to the authorities so that they can be destroyed!", "I'm covered in pig's blood!", or, "Are you busy Friday? We need a willing victim for our ritual sacrifice" would prompt some questions. They don't. They are so determined to see a TV show for little girls that that's what they see, regardless of what's in front of them.