Changing clothes in my car has become a very common occurrence. So has peeing in the parking lot but that's for a different post.
I'd guess that I change in my car just about as much as I do in my own home. And as good as I am at changing in the car, I've never attempted to change from my work clothes to my bike clothes while driving. I can't imagine what would happen if I tried that. My friend Adam does it all the time. I've witnessed it. Not the actual changing but I've watched him get in his car fully dressed in normal clothes, and then follow him in my car to the trail head, and see him pull up in his car fully dressed in bike clothes (bib shorts and all). As if he were a caterpillar who miraculously transformed into a colorful butterfly.
It's amazing really. I wish I could do that. But I lack the skills.