e.g.
https://www.bbc.co.uk/news/uk-scotland-highlands-islands-457...
"Cairngorm Mountain Rescue Team said the walkers' attire had included shorts and leggings, but no jackets."
I've never actually said to people I've passed that I thought they were inappropriately dressed (though maybe I should do) - but I have given people maps and directions when they admitted they had no idea where they were or their phone batteries had died (I take backup printouts of maps so not a big deal to give a copy to someone).