Also people who park their shopping cart two abreast with someone else, totally blocking the aisle. Or across the entrance at the head of the aisle.

And what about those go through the express lane with 20 items in their cart, right under the sign saying “10 items or less”? I look them in the eye and say, “Wow, you must have a lot of fingers!” I don’t know which pisses me off more—the shoppers who do this or the checkout clerks who let them get away with it.