I watched a particularly foolish driver the other afternoon who decided to cross over two lanes of traffic in order to prepare for a left turn about a kilometer ahead. This driver zoomed across all the lanes without pause, ending up in the left hand lane about three vehicle lengths ahead of a heavy truck.
To make life really interesting for the truck driver the next thing this driver did after making the lane change was to apply the brakes.
This unthinking driver put the trucker at a disadvantage, forcing his vehicle into a space that was inadequate. Compounding the problem was the brake application at a point where the truck had no place to go and no distance to stop. I don't think I could have picked a better example of how to make an unsafe lane change.