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Something that happens surprisingly often when I'm driving on the freeway:

I'm in lane 2 (where lane 1 is the leftmost lane, and this is usually on a four-lane freeway), behind a car that's dawdling along at, say, 10 mph below the speed limit. Say the speed limit is 65, and the car I'm behind is going 55. There isn't much other traffic on the road.

So I shift over into the leftmost lane to pass. I speed up to the speed limit. The car that I was behind also speeds up to the speed limit. I speed up past the speed limit. The car that I was behind does the same. We're now more or less side by side, going faster than the speed limit; say 70 mph.

So I drop back and shift back into lane 2, behind the other car, figuring we're now going at a reasonable speed.

And the other car slows down to 55 again.

And we repeat this cycle three or four times in a row.

This happens often enough that I'm reluctant to attribute it to malice or obnoxiousness; I don't think the other driver is doing it intentionally. But it also happens often enough that I'm reluctant to attribute it to random vagaries of speed. (Though I suspect that a fair number of other drivers value consistency of speed less than I do.) I'm at a loss as to what's going on, or why it happens so often. (Maybe once every couple of months?) And it's been happening for years.

So I'm curious: do any of y'all run into this sort of thing? And if so, do you have an explanation for it?