Re: Simple solution
Personally, in most cases I'll use DD-MMM-YYYY (e.g. 12-Jan-2020) or some close variant, which makes sense to everybody (well, English-readers, anyway) while being unequivocal and brief. If it's a filename or something else that needs sorted I'll use YYYY-MM-DD or similar (if it's likely to be sorted I'll use leading zeroes as well). Obviously if a form specifies a format I'll use that format. Sometimes if I'm filling in USian paperwork I'll use MM/DD/YYYY, but only if it makes sense to, and I'm always conscious of it.
I grew up with MM/DD/YY but I've experienced considerable enlightenment since then.
But I will give up my weird measurement units when you pry them from my cold, dead hands. The metric system is the work of the devil! My car gets 82 rods to the hogshead, and that's how I likes it!
We need an icon for Old Man Yells At Cloud.