It’s fascinating to see people suddenly accelerate after miles of the same speed on a relatively empty road because I moved into the passing lane, or (conversely) slow down because they’re alongside a slow vehicle and not in danger of being under-passed by another driver.

This is why if I'm on a road with one lane in each direction, when I pass, I PASS. Nothing is more terrifying than when someone takes their sweet time passing, barely going faster than the car in the lane next to them. Plus then you have to deal with the people like you're describing. They don't want to go as fast as you, but they do want to prevent you from passing them.

What I've found is that this type of passive aggressive driver is also a coward. Let's say they're going 60 and I want to go 65. I come up behind them to pass. If I try to pass at 65, there's a good chance they'll increase their speed to 65 in order to prevent me from passing them.

I don't give them the opportunity. As far as I'm concerned, when you're passing in a lane of opposing traffic, speed limits don't exist. If I'm risking a head-on collision, I want to get in and out of that lane as fast as possible. So instead of going 65 while passing, I'll rocket up to 85 and rapidly pass them. The passive aggressive assholes are cowards and won't speed up that much to prevent you from passing. So I rocket up to 85, get the passing over with before they can do anything about it, and then slow down to the speed I actually want to travel at. By that point, the slowpoke is well in the rear view mirror. They don't tend to speed back up either. By then their monkey brain just sees you as another car on the road, far away from them, not a challenge to their ego.