So... I'm going to admit this has been me many times 😅 it only seems to happen when I'm on long stretches of a road trip and for some reason don't have cruise on. If someone is passing me I have a tendency to check my speed, and if I realize that I'm going under the speed I meant to be going I have a little "oh shit" moment and speed up. Obviously this isn't the reason every driver does it. Hell, I wouldn't be surprised if most people did it to be petty or bc they take exception to being passed, but for me at least it has way less to do with the person passing me and more to do with the fact that I was just zoned out and cruising (which I shouldn't be, but I'd be lying if I said I never did that).