My interpretation is that Bletleyite is overtaking a car. He aims to leave a safe gap before pulling in in front of the overtaken car. However, the driver of the German car behind is annoyed by this, so pulls into the space Bletleyite is leaving before pulling over, then undertakes Bletleyite.
That's one. But more common is a situation on a fairly busy motorway when I pull out to overtake a car, but that car is too close to the car in front for me to safely pull back in applying the Two Second Rule then back out for the second one, thus the only safe option is to overtake both vehicles. However Mr BMW* prefers to pull left despite there not being the spacing for this to be safe, undertake and pull back in front of me.
It is however quite "fun" if they do this and misjudge it such that they end up stuck behind the second car.
Another one that I don't like is when I'm in lane 3 overtaking a lorry in lane 2 which is itself overtaking a lorry in lane 1. The lorry pulls back in, and as I said I won't make a manoeuvre alongside another vehicle also making one because it removes their ability to abort if they need to (or worse they may not see me there, might abort anyway and so sideswipe me), and I can't see lane 1 so can't judge if they may or may not need to. The BMW, as it almost always is, takes exception and zooms past my inside before I can safely make my manoeuvre once the lorry has safely made theirs.
Similarly if I'm overtaking in Lane 3 and move back left, said BMWs like to squeeze past as soon as there's only just enough space, which removes my ability to abort and is not appreciated. Before they pass they should wait for me to complete my manoeuvre fully so I have completely left the lane.
It's all just impatience.
* Always male, and always a premium German car, though Audis are almost as common as BMWs.