Education is the answer, not confrontation
I occasionally get a lift to work at one site from a colleague - and previously used to get a lift to the same place from a different colleague who has now moved on to a new job elsewhere. Both know that I cycle, and that I sometimes cycle to that site although the route is pretty meh, with rubbishy sightlines and narrow lanes and patches of truly shocking surface and far too much speeding traffic, including quite a lot of HGVs. With both I had conversations at various pointsabout why cyclists don't and shouldn't ride in the gutter* and why we will sometimes choose to take a strong primary** and so on.
Both commented a few weeks afterwards that they'd been looking a bit differently at the cyclists they'd encountered, and the roads they were cycling on, and now they understood. Last week I had a conversation with the very kind colleague who currently gives me an occasional lift about riding two abreast and she had a bit of a light bulb when I explained the 'half the length of overtake, half the time to complete the manoeuvre" thing...
*"Look at that massive pothole there, the one that you can feel when you hit it in the car - if I hit that on my bike it'd probably have me off and sprawled in the road and that would really delay your journey!"
**"See this series of blind corners? If someone overtook a bike here and there was an oncoming vehicle is there
any way at all to avoid an accident? See, that's why I go right out because then nobody can try to 'squeeze' past."