It's often the case that I'm waiting in line behind people who don't know how to use a self-checkout machine. I feel no undue hated towards them. The user interface of those devil devices is awful, and it seems like every change to them just makes them more awful.
I've never before been in line behind so many people who didn't know why to them, though. Yesterday I was shopping on the way home and had to wait while four people separately clammed up the self-checkout machines with trolleys full of stuff.