Paying for merchandise is OMG srz bznz.

So, at my stores Point of Sale, we just implemented a new function where WE (the lovely cashier) have to approve your total before we can accept any kind of Tender from you. This includes CREDIT and DEBIT cars which Hey! Whaddayaknow! You can use yourself at the keypad on the counter and it is so convenient and magical and wunderful and omg awesome and WHY IS THE CASHIER GLARING AT MUH?!?!
Well, probably because while I am still ringing up your purchases, you are frantically swiping your card enough times and with enough urgency to make me wonder if perhaps you have planted a bomb in the building. Turning wildly to me and screaming "It won't work!!!!" will only elicit a DUH from me, because, you know, you can't pay for stuff while I'm still scanning items!!! Common sense, people! GET YOU SOME.
Oh, and it's always these people who are in a such a hurry to, ugh, just get this thing OVER with already, come on, what's taking so long!, who then stand there for five minutes studying the receipt with enough cautiousness that makes you wonder if in a previous incident one of these newfangled things has turned into a cobra and ATTACKED THEM.
Also, If I'm taking an ungodly amount of time finishing your sale, it just miiiiiiiiiggggghhhhht be because you brought me 15 breakable items and wanted them all wrapped in paper and put in separate bags. So don't stand there and stomp your little last season prada shoes at me, honey.