A customer approaches counter, gets card out of his wallet, before finally realising the coffee shop is closed.

So he puts back his debit card, paces several paces back, and shouts abuse saying I should have told him about it being closed.

Instead of being humble realising it has been closed for some while, he was just too distracted to have noticed, the customer reacts as if the unit was suddenly closed as he was walking up.

Wait, digital menu screens are all off, lights are off, condiment bar put away blocking the hand-off area, the A board is in physically blocking access to the till area and the till screens read "CLOSED"... what made him think it was open?!

Why did he feel the need to resort to abuse?

I wasn't helpful here - hottest day of the year, end of a long busy tiring shift and behind on so many tasks. Speaking with customers needs to be polite and represent the brand ethos, but doing so forms a queue, and everyone wants to speak to me. The visual clues, in addition to hearing me tell the persons immediately in front that we are closed, doesn't dismiss the rest of the queue, as you might presume.

They want their turn and sometimes think a specific drink or approach of asking (including flirting) unlocks the ability to order or get a freebie. Tills are closed for the day (not to mention inaccessible) and coffee machines are going through their cleaning cycle... not to mention I am busy!

Letting adults join the dots rather than a forced 3 minute conversation with everyone (which could yield a bad review if I seemed too dismissive, annoyed or rude by not wanting to have 8 or 9 identical conversations) seems reasonable here.