It really depends on the type of humour. I don't think it's so much that I don't get the joke, but just that I don't find it very funny.
For example, I don't find racist/sexist/homophobic/ablest jokes very funny, but I know they are "jokes". I dunno, it's just not my type of humour. But jokes related to politicians, I find EXTREMELY funny. Even if it's one I support. I think this is true for most people (that they have a preference for certain types of jokes).
For sarcasm, I'd say I understand it. I'm not a fan of it, unless it's in a joking fashion meant to be funny. If it's just meant to hurt someone's feelings, no, I don't like it.
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-Allie
Canadian, young adult, student demisexual-heteroromantic, cisgender female, autistic