Only say things that can be heard. If you can anticipate that you are too many inferential steps away, you should talk about something else. Which means in this case: Be patient and build their knowledge from the bottom, not from the top.

If you have already started and notice the problem too late, yeah, you're kinda screwed. The honest answer seems pretty rude, and not saying anything is worse. I'd probably try to salvage what I still can by saying something along the lines of "I know this is a complicated and confusing issue, and it takes a while to explain where I'm coming from*. I can point you to these resources if you're really interested in the matter." And not bring it up again unless they start it.

This allows you to drop a conversation that's going nowhere, while they can research it if they want to or ignore it if they don't while still saving face in both cases.

*Or, if it went really bad: "...and I suck at explaining." - taking the blame for the failed communication can defuse the sting of making them feel stupid.

This post is about my horrible social skills, I'm not complaining about other people's behavior. My main life focus right now is on learning to communicate better.

Try to ask questions that probe for the reason they don't understand (rather than assuming you know the reason), see if you can reformulate your point as an analogy that makes sense given their level of knowledge and doesn't require all that context?

(A little hard to answer in general without knowing more specifics of the situation.)