I didn't get into specifics before, but even concrete examples as a backup have failed. They'll listen and understand the example on a narrative level ("this is a weed to Person 1 and here's why, but not to Person 2 and here's why,"), but every fibre of their soul is clearly trying to ask indirectly: "okay, but how are weeds defined then?" It's like you'd think they're trying to square a scientific disagreement between Persons 1 and 2; it's like they're trying to figure out who was right.

What's especially crazy to me too is that this has never, I think, been in the context of me challenging what they consider weeds and suggesting they reconsider; it's just come up sometimes. I'm handing them the absolute, irrevocable right to keep their categorization of weeds exactly the same, but they act like a cartoon character trying desperately not to remember they're walking on air.