They also tell the cashiers that their family will be killed if they don't process each item at at least Mach 1. (Or that's what it feels like at the checkout anyway...)
You have not know humiliation if you have not experienced a line of slightly elderly shoppers mildly frowning and tutting as you hurl your items into a bag, whilst the cashier looks at you with overt disapproval. The only accepted bagging speed is “Superhuman” and the best day of my life was when the cashier at my regular Edeka nodded approvingly at the fact that I was practically ripping the groceries out of their hand as soon as the cash register beeped.
Supermarket staff here in Italy, where I now reside, think I am insane, and I work hard to contain my impatience with those lesser-trained people in front of me at the cash register.