Usually no, but if I'm in a car and notice the driver has a dangerous habit, I will comment on it. I've noticed most people get annoyed if you criticize their driving, especially in their own car.
My ex-girlfriend would follow other vehicles very closely, even at high speeds. I would tell her to stop tailgating, and she'd say "I'm not tailgating, this is just how I drive". Not only is that unsafe, but it's bad for the car too because every time the vehicle in front of you slows down you have to step on the brakes, whereas if you leave a bit more space then you don't have to brake to accomodate their every speedup/slowdown. That's why she needed a brake job almost every year and I can go more than 5 years without a brake job. Also, if you follow too closely then every rock/pebble their tires kick up bounces off your paint. Also, she wouldn't bother evading potholes, which is another thing that irked me.
I think the large amount of cycling I do has made me a much better driver, both in terms of safety, and in terms of how well I look after my car.