Meanie
If someone writes a check, or uses ten different prepaid cards to pay for one purchase, or argues over a coupon worth fifty cents, I try to be patient. Perhaps they're in a bad cash situation
What kills me is when a customer in front of me waits until everything is bagged and ready to go, before acting surprised that they actually have to PAY, and ONLY THEN start to rummage through their purse/bag for a card. Myself, I swipe my card at the grocery checkout the moment my first item is scanned, so I'm ready to pay the instant all is done. (An action which is not possible with contactless or chip cards.)