Turns out his entire family (both parents and at least his sisters; dunno about his brother) all have a weird ambiguity thing, only they consistently guess wrong. We had not ever noticed this until this trip, and came to this conclusion after thrashing out several conversations that had occurred over our Xmas visit.
The general format of one of these conversations is: O. (family last name) asks a question (like, what does T. like to eat). I attempt to answer (by listing some of the things he likes to eat). A very short way into the list, O. interrupts and attempts to summarize the category of things T. likes to eat. Really, there isn't an accurate summary, so I propose numerous additional things that do not belong to that category. O. does not feel heard and figures out a way to wrench those items into that category. I get frustrated and angry because I can't figure out what the hell happened, and start looking for a graceful way out of the conversation. O. follows me around persisting in misunderstanding because they do not feel heard. Etc. By the end of a given trip, I basically would like to beat the shit out of the entire group.
Lately, I've taken to working very hard to never, ever, ever answer a question from one of these people, because it's so freaking hard to communicate with them. As long as they're talking and I'm responding with short little, I understand what you are saying kind of remarks, everything is good. I've also quit trying to get clarification when I don't understand what they are saying, because that's a disaster, too, and they talk enough that if you just wait them out, you can usually figure it out. If you can't, you can ask their spouse later, and they can explain because they don't suffer from this problem.
Might be genetic. Weird.
The new theory/strategy is as follows. They ask me a question. I answer. They summarize incorrectly. I make sure they feel like I understood what they said. When that's extremely clear, I say, as bluntly as humanly possible, that is very interesting and I'd be happy to talk about that, but that isn't what I said, then let them choose whether they'd like to hear what I said again, or would rather talk about whatever other crap they introduced into the conversation. And don't be in a hurry to get through a story, because these people are far too fucked up to understand anyone outside their family, and may or may not be doing well within their family.
R. suspects this is somehow related to why they are lawyers.