Via TJIC, I meet this guy on every long distance trip.
Apparently, there are some people who: A) Cannot judge their own speed except in relation to the vehicle directly in front of them, and B) Cannot hold a steady pedal for love nor money. So there we'll be, in the agrarian hinterlands of Indiana or Kentucky; me rolling along in the left lane and passing the occasional car on the right when I notice Mr. Wobbly Throttle a'creepin' up in my mirrors. When he gets close enough I'll signal right and let him pass, which he does, after a fashion, but sort of bogs down once he's just off the port bow. We'll roll in formation like that, me starting to fume, until we come upon a car in the right lane that forces me to turn off the cruise and tuck in behind Wobbly.
As we pass the slower traffic, Mr. Wobbly Throttle, now bereft of vehicles to overtake, starts to slow down. He notices me in his mirror and sometimes darts right, sometimes slows down further and gets passed on the right (traffic gods, forgive me!) I'll hit "Resume" on the cruise control in the left lane, but a mile down the road, sure as God made little green apples, here comes Wobbly again, as though drawn to a magnet in my back bumper. This dance can go on for over a hundred miles, and is pretty well guaranteed to have me chewing the steering wheel in frustration in only a fraction of that distance. For Vishnu's sake, man, pick a speed and hold it!