And if you're wondering which item causes the most problems, it's milk. O'Herlihy explains, "People find it hard to scan milk ... Sometimes they get frustrated and they just don't scan it."

Does milk not have a bar code?

If anything, I’d figure it would be produce items that would cause the most drama, but eventually you start to remember those codes. 4011 is bananas. 4799 is for tomatoes. 4065 is green peppers…

I love self-checkout because I bag things exactly like I want and I can get the process completed without having chat with the cashier or Karen out on the bagger for putting just two items in a large paper bag.

I don’t think I’ve ever been stopped or accused of stealing things, but then I usually choose the unit closest to the cashier and I leave all my items in the bagging area until I’m done. That said, I used to be a grocery store cashier, so I understand the process a little better than most, but it’s still easy to make mistakes.