It is a the worst sin a restaurant customer can commit.
Worse than turning up for a table for four with diners suffering from three different food allergies. Worse than sending barely-eaten plates of food back to the kitchen. Worse than being rude to the waitstaff.
The behaviour that infuriates restaurateurs more than any other; and costs them more more money than any other, is the growing habit of not showing up when you have booked a table.
You wouldn't think it would be that hard to make a quick phone call to say your plans have changed; or that you have a personal emergency and won't be able to make it.
But staggeringly, up to 5% of all restaurant bookings result in what the industry calls no-shows.
That might not be a catastrophe on a quiet Tuesday night, but on a busy Saturday a table of six might spend $800 or more - and losing that income can be a considerable financial blow.
Multiply that by two or three tables several times a week and restaurateurs are hurting in a tough, competitive environment. And it is not just the financial loss; staff can be left standing around with nothing to do if two or three tables of diners fail to turn up. But they still expect to be paid for their time.
Now restaurateurs are hitting back at the growing lack of manners. Some have taken to sharing the names of the no-shows with other restaurants in their area. Others shame the guilty parties on social media.
Now, more and more restaurants are demanding credit card details with every booking. And each no-show will result in payment if you do not have a good enough excuse. Because many eateries have waitlists and can call up replacement diners event at the shortest notice.
And why not pay? If you miss your flight from Sydney to Melbourne you still have to pay for your ticket. You certainly pay for your cinema or theatre ticket even if you are stuck in traffic or your plane is delayed.
Australia’s largest on line restaurant booking network, Dimmi, has sent a warning to diners. “Enough is enough - either show up for your booking, or face being banned.”
Australia has lagged behind the US and the UK in imposing sanctions on no-shows, and there are plenty of stories, perhaps apocryphal, about groups of diners who book at two or three fashionable restaurants and then decide on the night which one they fancy attending.
So. Coming soon to your favourite eatery: a per-head credit card charge if you don't turn up, or the payment of deposits to guarantee you do show up.
It is a serious problem - and the restaurant industry is finally addressing it seriously.