This is one of my most hated things on the roads.
Last weekend I was driving back home to Melbourne from Albury. I was in the right lane, behind another car, as we passed the slower traffic in the left lane. Out of nowhere one car in the left lane suddenly pulls out in front of the car in front of me doing about 95 in a 110 zone. It was a tight squeeze, forcing the car in front of me to slam their brakes on, and then obviously also slowed me down. He finally sped up a little and eventually overtook the truck in the left lane, then pulled back into the left lane. I re-activated cruise control and picked back up to the 110 speed limit, pulling back into the left lane when it was clear. A couple of km's down the road the same guy that slowed us down was tearing past me in the right lane?? So frustrating.
My main reason for getting frustrated with people that do this is that I like to cruise along with cruise control on. It's simple, cruise in the left lane at the speed limit, pull out to the left when necessary to overtake, then back in the left. I never have to touch the pedals, don't have to worry about watching the speedo for my speed. Then you get the idiots "holding hands"... ie, two cars taking up both lanes driving steadily next to each other. I have to brake, slow down and wait patiently for one of them to get out of the way before I can "cruise" again. It's just annoying.
A few months ago on the freeway I saw a police car come screaming up behind me in the right lane. They passed me and just ahead of me was a car in the right lane, with nobody in the left lane anywhere near them. They stayed in the left lane for at least 1km with the police car right up their ass with lights and sirens blaring. Luckily for them, the cops weren't after them, just simply looking for a spot to pull a u-turn on the freeway, but far out! How could you not notice a police car behind you for that amount of time with lights and sirens going? Surely that would hint to you that you shouldn't always be in the right hand lane unless overtaking!?