Not the one you're replying to but my SO was a terrible driver and still has issues. At first I brought it to them calmly but over the years it turned into nagging. That being said, their driving has improved significantly. Much safer than it was but they still get mad at other cars who were being oblivious. They also admitted they have problems seeing at night so I always drive at night now.

They're aware I have a problem with their driving and it is a source of contention in our relationship but not enough to break up over.

I deal with it by being the one to drive more than 99% of the time. It would be a problem if he wanted to be the one driving, but fortunately he doesn't.

I don't know why he tailgates. He doesn't recognize that what he's doing is dangerous. So I guess stupidity....

The last time I was a passenger in my brother's car, I remembered that he tends to drive in a way that makes me feel unsafe, like what OP described. Unreasonable acceleration, tailgating, swerving. He laughed when I was physically bracing myself and said his partner does the same thing. I told him I just won't be in a car when he's driving anymore. Of course, it's easier to do because I don't see him too often.

IMO when I'm driving, I not only have a responsibility to keep my passengers safe, but to make them feel safe. I might feel safe because I know I'll brake in time, but my passengers don't because they're not controlling the vehicle.