Sarcasm is part of the Use (pragmatics) section of language communication.

In *some* people with communication disorders, stemming from a variety of reasons (eg, autism), their ability to understand these social rules can be lessened. Figurative language (sarcasm) is here. + https://twitter.com/jae_day6/status/1315403480735989760

People who have less skills in this area of communication, will often take what is said to them literally. For example:
“It’s raining cats and dogs” - no, it’s raining water.
At work: “Can you serve that customer?” No, I’d rather not.
“Well that was smart” No it wasn’t! ++

Over time, people can rote learn these more common sarcastic phrases so they are prepared when they come along. People with less skills in social communication can have difficulty reading emotion, context, tone of voice and facial expressions ++

When you think about sarcasm, it is heavily reliant on facial expression, context, emotion and especially tone of voice. For someone who has difficulty reading those cues? It can be impossible to understand sarcasm. ++

It is not the best example, but think of sheldon cooper from Big Bang theory. I hate using that example but think about how he reads his friends, and therefore his lack of understanding of sarcasm.

Can we please get passed this notion of being dumb to not understand sarcasm??

Please note I use communication disorders in a completely clinical format, as a speech pathologist and do not mean harm to anyone - I am autistic and I also have difficulty with social language. In slp circles we do refer to this as a communication disorder though