Well, since you said: "Of course, I've entertained the possibility that they might not understand what I say b/c it's not relevant to the central theme of the discussion (at work mainly).....", I'm thinking their saying: "I don't understand" MIGHT mean "I don't care", or "What does that have to do, with anything"; and your repeating yourself, in hopes of getting them to understand, only makes it even MORE frustrating, for all involved.
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White female; age 59; diagnosed Aspie.
I use caps for emphasis----I'm NOT angry or shouting. I use caps like others use italics, underline, or bold.
"What we know is a drop; what we don't know, is an ocean." (Sir Isaac Newton)