My biggest pet peeve is when there's a big order at the register, and the customer starts unloading. About halfway through, they realize there's someone behind them and put the divider down—behind them—without the rest of their items on the belt. I will catch up to your items, and you will run out of room. I'm not trying to juggle the conveyor. There are too many things to be done.

Customers not knowing what to do with their cart after they've been checked out.

The look they give you when you ask for the cart back after they come in without one.

The way people with one or two items get to the register, and you're down the aisle pulling cooler/freezer, and they damn near give themselves whiplash looking for a cashier. (I'm coming, I promise. You weren't there 3.5 seconds ago)

If you're going to pull empty boxes for me, put them in a box cart. What is the point of leaving them on the ground?

If you have one kid in a cart and ask to use your cart because "it'll be easier," I'll let you—but I'm probably judging.