For me I get irrationally pissed off when a world has one mythos but insiders react like other mythos are silly and completely illogical.

For every "Charmed" or "Once Upon A Time" where everything has a root in some sort of magic and every story has an ounce of truth there are stories like "The Sarah Jane Chronicles" where one time when traveling back in time a maid was being haunted by a ghost. Sarah Jane's response. "Don't be silly, there's no such thing as ghosts. It's obviously an alien" for 3 days I hated Sarah Jane Smith. I've seen it a few times where there will be a world of magic but then a wizard will scoff at the idea of a leprechaun being real.

It's different when for instance people cling to what they know such as in "Agents of SHIELD" where one of the scientists refuses to believe in ghosts because so far everything has been proven with superheroes and super-powered aliens*. I find that annoying as well but I don't find it maddeningly so. Or occasionally we'll get something like if i remember correctly The Mortal Instruments series has referenced certain mythos as unconfirmed (Zombies i think?) but at least they aren't just dismissing it off hand like it was a stupid question to ask.

E: forgot where I was and I realize this post is mostly fantasy examples. I meant to post this in a SFF context because while i do see this in sci-fi, I see it more in fantasy. Unfortunately I can't really change it now and I would argue for the micro relevance of my post and the macro relevance of my title.

E: * - to clarify my point to my recollection it turned out spoiler