Children in primary school tutoie their teacher and call him/her by their first name - they learn that when they go to collège at 11 they call their teachers madame or monsieur and vouvoie them, and are hugely embarrassed and get les gros yeux from their teacher if they slip up. That’s why inadvertent tutoiement isn’t too dreadful, from that age-group, even though strangers will pick them up on it, nicely or sharply.
But at the same time outside school they are taught to vouvoie anyone new they meet, family friends, people in shops etc just as they learn to say bonjour Madame or bonjour Monsieur when they go into a shop and au revoir when they leave it. It will be mentioned to them by some adult if they don’t.
We are taught this from the time we start walking, pretty much. It is very much ingrained in our culture - which is why we expect someone who speaks French well to have taken it on board and to make the effort.
Just because people are nice about it doesn’t mean they think it is acceptable and they expect you to feel embarrassed (because they would in your position), which is why they say it is cumbersome to vouvoie, in order to salve your feelings. Nobody will take you to task the way they would a French tween because it wouldn’t be polite.
I’m actually doing you a favour by explaining this, I’m sorry if you feel it isn’t polite.
Is there a threshold size of shop where this is no longer required - I got some funny looks at Auchan Bordeaux Lac as I bellowed Bonjour on arrival just loud enough so that everyone at the back would hear.
I say bonjour to the guard inside Leroy Merlin and again to the lady at Reception…
at the local butcher… I say bonjour gently… either directed at the others waiting… or to the person who will serve me…
going into Gemo… often someone will call out and I will reply… and as we customers pass one another… a smiling nod of the head and/or a gentle bonjour…
Round here, in small shops murmuring “M’sieur dame” on entering finds favour. And NOT smiling while doing it. In fact the more miserable while doing it one can look the better.
Oh dear. In our village shops I always “Bonjour!” each and everyone far too heartily with a gigantic smile and even a little bow to children. I wonder if my village think I’m a few shillings short of the full pound?
By all means continue, provided it’s done with a scowl. Also, when giving way and they too move to one side on the grass verge, lift one finger off the steering wheel to say “thank you”.
Ha ha… I smile politely at everyone… even if staying silent… always have done…
and, generally, folk smile back…
as for waving… I’m hopeless at recognising a vehicle.
Friends would admonish me… why didn’t you wave… ???
so now I have it off pat… I raise my hand as if protecting my eyes from the sun… as I peer at the traffic…
if the driver attempts to move a hand or flash the lights… I can swiftly throw together an energetic wave… hurrah.
With covid, folk have been even more willing to wave… whether on foot or in a car…
who’s that?? no idea… but they waved so I did too…
If I know folk very well… they get my full main-beam…
If I don’t know folk or know them only slightly… they get my “polite” smile.
In all the years we’ve travelled, for business and/or pleasure… we’ve never found anyone (in any country) take offence at a polite smile… quite the reverse.
I wonder if that is similar to the ancient English expression “knock in the cradle” ?
Round here some people do that but the older farmers tend to do what we think of as the Normandy nod - an unsmiling lifting of the head, like a nod in reverse,
It comes from the Santons who are little traditional figures from Provence in the crèche, le ravi marvels at everything because he is an innocent happy with everything, but especially at the arrival of the baby Jesus. So his wits have been ravished and it means the same thing pretty much.
Thank you @vero. Most interesting to understand where these things come from! I’m also understanding more of the origins of English words since I’ve been grappling with French
Thats fascinating @vero. It prompted me to look further at what happened to the informal ‘you’ (thou) in English, which seems to have fallen completely out of use by 1800.
I learnt years ago that smiling at complete strangers, especially if they are elderly farmers, makes them nervous.
Also, when giving way and they too move to one side on the grass verge, lift one finger off the steering wheel to say “thank you”. 
as I peer at the traffic…
and it means the same thing pretty much.