There's an elephant in the room here though: curtesy is rude when it robs the receiver of the opportunity to be righteously angry that no one ever helps them.

You never know when someone is setting up a situation because they want to complain about the hardship, tell their friends later that bystanders/shop assistants/other drivers didn't help and generally have a little martyrdom. If you offer them a courtesy of any kind during one of these episodes, you're actually ruining their game and dealing out a cruelty to them.

Edit: if you've seen how angry a middle aged woman not getting served in a posh shop is, just you wait until you see a middle aged woman who approached a posh shop certain she wouldn't get the correct service *then did*. The Horror. To be robbed of shopping centre martyrdom. How humiliating.