People who won't go past a truck on a multi lane freeway.
For example, pulled out onto the Monash from an on ramp. I'm behind a car doing 90 in a 100 zone (bad enough) but still enough to creep up beside a truck in the lane next to them.
They jump on the brakes and slow to about 78-80, simply terrified to drive past the truck, sitting on its left rear tail. I'm stuck behind them, can't get out behind the truck because everyone else is running up its arse, and this nanny in front of me just refuses to go past the truck, continually jumping on their brakes.