The short answer (besides telling you guys to look it up...) these sorts of conditions can make it so the person can't be sure of a literal or serious statement, from sarcasm, and other forms of joking... they quite literally, take things quite literally...
It's a little bit like the difficulties most of us have when deciding if someone is being snarky in writing... or meaning something other that what was written... as opposed to say... when someone is right in front of us, saying the same thing... there's many additional cues/clues like body language and facial expressions to help us gauge the intent or meaning... Unfortunately for Auties, and Aspies... those cues/clues aren't necessarily interpreted appropriately (or as intended) even in person...
Just imagine when we take things the wrong way... Now imagine... not really knowing what the right way, out of several possibilities is on a frequent basis...
Is it gas... or is the baby smiling at you?
Do some reading... learning is accepting... understanding is helping...
-Marka