re: What really grinds your gears.

People being checked out at the grocery store aren't ready to pay. The cashier gives them the total and they look all surprised that they actually have to pay and spend an inordinate amount of time searching through a purse .

Cashiers who can't talk to a coworker and ring you up at the same time. During the middle of checking you out another cashier or coworker may say something and your cashier continues the conversation while she stops ringing you up.

People who who won't turn right on red despite there being 200+ feet of a merging lane. Old Perkins at airline by the Walmart is a prime example.