Here we have an example of something that happens pretty commonly on Montreal's roads. There's a single lane merging onto the highway and a long lineup of drivers patiently await their turn. Then some asshole decides that his time is more precious than everyone else's, so he should be able to cross two solid lines and cut in ahead of all the other cars.
This can be frustrating and although most people remain polite, sometimes you just don't want to let those entitled jerks win. So you stay close to the car ahead of you to prevent them from cutting in and it usually ends there. They either sneak in behind you or they catch the next on-ramp. But sometimes, the entitled assholes feel this is unfair and they decided to throw things.