Remember that unobservant and/or entitled asshole driving the SUV? It turns out our assessments of other drivers, along with their motivations, are also often painfully simplistic or flat out wrong. Maybe the SUV driver had to quickly swerve to avoid a piece of road debris you didn’t see. Maybe you were the asshole, riding in his blind spot and being too preoccupied to notice that he did in fact use his blinker.
These possibilities don’t register while driving because we make snap judgements by consulting our emotions instead of our logic. You were mad, and therefore the SUV driver is an jerk.