Every time I go into Sainsbury's, people have to have the new bag rule explained to them (that you have to pay for the bag before you get one; apparently people were nicking them) even though there is a sign on all the self checkouts. Usually it only has to be explained once and the other people in earshot then get it, but I assume the process repeats every time a new set of people gets to the checkouts, all day, plus some people seem extremely dense.
"You have to pay for the bag first, I have to see the receipt and then I give you one."
"Okay." waits for bag
"No, you have to pay for it first. Tell me when you finish and I will look at the screen and bring one over."
"Ah ok right." waits to get bag
"No I can't give you one now you have to pay on the machine and I will check it and give you a bag."
(other customers sometimes chip in)
"Ohhhhhh! Riiiight!"
(Someone else who has not been listening): "Hi can I have a bag please?"
Today someone else in the queue just gave one guy a spare bag they had, to save time.