My father in law wees in my garden as does his brother, when they visit.
We don't have a downstairs toilet, just an upstairs one. It is not done when the toilet is occupied, they literally just go out the front door and wee rather than go upstairs. They're older (in their 70s) but not incapable of climbing the stairs by any means. They are from overseas and say this is common and acceptable behaviour in their country and nobody bats an eyelid about weeing in the garden. The uncle in law at least goes out the door and to one side (lucky neighbours) but FIL literally stands in the porch and pisses out.
I have made it abundantly clear that I find it absolutely unacceptable and disgusting, but they still do it, and think I'm uptight.