The fact that I can't order my sandwich ahead from the deli because of the incompetency. It would be very convenient for me to order ahead online and go pick it up but I can't do it because they get it wrong, the majority of the time.
I try to keep calm when I witness such driving. You have to be a saint or practice coping mechanisms to deal with it. Only the other day someone tailed me for 10 miles straight regardless of my attempts to lose them.