That happens a lot over here too. Most people are nice if the car in front signals to do a lane change just as the fast car is passing, but many aren't.

OTOH, I've actually waited behind cars that were stuck behind slow traffic only to find out that they didn't want to go to the left lane. After a couple of these, I decided that if the car in front doesn't signal, I'm going.

If you watch racing of most any kind the best drivers are very smooth in all their manuvers........
William Rogers.........