@thor
Problem here is, most of the time there will be a queue forming behind you. So you're likely to feel pressure from behind you to get done with your business as fast as possible. Which kinda forces you to say something if you even slightly think the cashier isn't busy.
And considering you also waited in the queue for a while, your patience would have already been tested.

Now maybe northerners have more patience reserves, that's very likely, but for us, because of the other circumstances, it just wouldn't work.